Some Iskcon devotees claim that Sikhism is Vaishnavism. Shri Gaur Narayan Prabhu has provided the following evidences that establish that Sikhism is not Vaishnavism, but possesses only a superficial resemblance (quoted from Akal Ustat of the Dasam Granth):
On the Sankirtana Yajna of Chaitanya Mahaprabhu
On the Avataras of Vishnu
On Krishna, the Supreme Personality of Godhead
Those sects that bear resemblance to Vaishnavism, but advocate Bhakti as a tool to approach the Unapproachable Non-Existence, the Nirguna Brahman, and Nama as a tool to overcome the Formidable Non-Existence, Maya, are called Bhagavata Mayavadis. Bhagavata stands for the methodological similarities to the Bhagavata tradition, Vaishnavism, and Mayavada for the aspirational similarities to the Advaita Vedanta tradition, Mayavada. Some examples of unorthodox Bhagavata Mayavadis are the Warkaris (Jnanadeva, Namadeva, Tukarama), Nirgunavadis (Kabir, Ravidas, Nanak), the Mahapurushiyas (Shankaradeva, Madhavadeva), some Apasampradayas (Aula, Baula, Sain, Darvesha, Kartabhaja, Neda Nedi), the Swaminarayans. Although these sects are part of the Hindu-Buddhist civilisation and the saints belonging to these traditions have brought life and song to billions in India, for an orthodox Vaishnava, they are bad association. They are more dangerous than orthodox Mayavadis because they create an illusion of Bhakti and then pierce the heart with the worst kind of blasphemy.
The Ramayats or the Sagunavadi followers of Ramananda, whose main text is Tulasidas's Ramacharitamanasa syncretise Shri Vaishnavism and orthodox Vedic Mayavada. They are respected within the Vaishnava orthodoxy, but ultimately they are also Bhagavata Mayavadis. Tulasidas was a great friend of Madhusudana Saraswati, the greatest Advaita philosopher after Adi Shankaracharya. Both lived in Varanasi. Indeed, when the Kashi pandits attacked the former for writing a scripture in Avadhi, the latter saved him and since Madhusudana Saraswati was the leader of all the Mayavadis in Varanasi, no one could harm Tulasidas. Together, these two great saints syncretised Vaishnavism and Mayavada. Interestingly, Madhusudana Saraswati writes that it is better to be a jackal in Vrindavan, then to attain the impersonal Brahman, although impersonal Brahman is the highest stage.
As a young man, Saraswati was greatly attracted to Chaitanya Mahaprabhu, but when he arrived at Navadvipa, Mahaprabhu had already left for Puri. So, he began his study of Navya Nyaya at Navadvipa, the seat of New Realism. After completing his studies, Madhusudana went to Varanasi, the seat of Idealism to defeat Advaita Vedanta. He enrolled in a school to learn the Purva Paksha, the opponent's arguments. However, soon, he was converted from Realism to Idealism. He revealed his identity to his Guru, who ordered him to accept sannyasa for repentance. After that, he emerged as the tallest figure of Advaita Vedanta and wrote Advaita Siddhi to defeat the great Vaishnava polemical treatise, Vyasa Tirtha's Nyayamrita. But the softness for Bhakti remained in his heart and he went on to write many books on the subjects of Rasa and Bhakti. Thus, Tulasidas and Madhusudana Saraswati fall into the category of orthodox Bhagavata Mayavadis.
Although Abrahamic religions have totally a separate background, there are ideas of Karma, Jnana and Sharanagati within them. Orthodox Jews, Christians and Muslims are Karma Kandis (those who aspire for enjoyment through worship of God). Houris are similar to Apsaras. Sufis, Kabalists and Gnostics are Mayavadis (those who aspire for annihilation through worship of God). But actually, Islam means Sharanagati, i.e., complete surrender of one's aspirations to the worship of God. So, worship is the only aspiration. Christianity bears resemblance to Tenkalai school of Shri Vaishnavism, which emphasises Grace over Work for Salvation. If Salvation means Uninterrupted, Selfless Love and Service to God, then the Abrahamic religions are also have properties of Vaishnavism.
However, since they do not follow the Vedic Path, they must go through the process of gradual advancement over lifetimes to understand the Names, Forms, Attributes, Pastimes, Abodes, Associates and other Paraphernalia of the Supreme Personality of Godhead. They may gradually advance by following their Natural Dharma. Those who say that the followers of the Christ and the Prophet would enter Vaikuntha forget that these people reject Vishnu and disrespect His Deity, as recommended by their scriptures. The best thing would be if they participate in the Sankirtana Yajna as recommended in Shrimad Bhagavatam. Then, they would immediately qualify to be called Vaishnavas. Otherwise, they must continue to follow their given laws, without clear conception about Karma, Jnana and Bhakti, and wait for God's Grace in the next life.
Now, what is the Sankirtana Yajna recommended in the Shrimad Bhagavatam and introduced by Chaitanya Mahaprabhu? Is it simply shouting and dancing? Mahaprabhu brought the bitter pill of love (it is bitter for a materialist or an impersonalist) coated with the sweet process of singing, playing (instruments) and dancing. Just jumping up and down, without cultivating devotional service is no use. We enjoy Kirtana, but not Japa because we are approaching the Holy Names with enjoying mentality, not serving mentality. Only by hearing from those who have love in their hearts, our dormant love can be activated. That is why, good association is necessary.
The Holy Name is always Pure, Non-different from the Holy Named, God. If one has complete faith and is free from all offences, only then one can pronounce Shuddha Nama, Pure Name. If one has no faith, but pronounces the Holy Name (symbolically, jokingly, contemptuously or indifferently), it is Ashraddha Namabhasa. If one has incomplete faith, but is trying to pronounce the Name without committing offences, it is called Shraddha Chhaya Namabhasa. Trying to avoid offences produces Chhaya Namabhasa, actually being offenceless produces Shuddha Nama, but deliberately committing offences gives Pratibimba Namabhasa. Pratibimba Namabhasa is also called Namaparadha. One deliberately commits offences only due to perverted faith. Mayavadis have perverted faith and knowingly commit offences against the Name, so they are Namaparadhis. Vaishnavas have natural faith (complete or incomplete), so they chant Shuddha Nama or Namabhasa.
Nevertheless, we see that Mayavadis happily chant throughout their lives, while many Vaishnavas burn out eventually. It happens because sincere devotees are trying to remove offences, trying means repeated failures and as a result, offences pile up, overburdening the devotee. But Mayavadis happily commit offences due to perverted faith and that makes their chanting relaxing (they are not trying to remove offences, a burdensome exercise). Hence, a devotee should approach a Guru, who takes away our offences through his instructions and discipline. Without a Guru, an independent devotee, unless almost completely pure, would be collapse under the burden of his offences.
Actually, Namaparadha gives little benefit. The Lord feels like it is an abuse to His devotees. The Namaparadhis never get burnt out. Krishna gives them opportunity to commit more offenses, increasing their sense gratification, leading them to sin and ultimately, to hell.
Those who do Ashraddha Namabhasa, like the ordinary people, Muslims or Hindus, get some benefit and accumulate Ajnata Sukrti, which leads to appreciation of Bhakti within their hearts in the present or a future lifetime.
Those who do Shraddha Namabhasa fight against the offences and deepen their faith. They receive the Lord's blessings through proper guidance of a bona fide spiritual master. They quickly clear their offences and advance to the stage of Shuddha Nama.
The rare soul who chants the Shuddha Nama gives bliss to the Lord, who in return gives Himself to that devotee. Such a devotee quickly advances to the highest stages of emotion and mellow, the Name reveals to him the Form, Pastimes, etc. of the Lord, and he attains the Pure Love of the Supreme Personality of Godhead.