Practices which are exclusive with Muslims is proof of Islam provided there is no absolute daleel of kufr. If there is any absolute factor (belief/practice) of kufr, the ruling will be kufr. (Example: A person who performs Salaat wears a cross or also prays in a church or does not believe in the Finality of Nubuwwat).
[Malfoozaat Hakeemul Ummat]