This is a quick one,
There are many questions as to whether God provided another paths of salvation. I don't think there are any except Jesus but I am sure that before Jesus He has send many to point to Him but except they sort of garbled up the message for Paul has said God did not leave Himself without a witness.
I am inclined to think that Guru Nanak the founder of Sikhism and Muhammad, founder of Islam did hear from God....they were from polytheistic societies and all the sudden they go monotheistic...however due to human nature and pride the message was diluted and polluted and in time to to peer pressure the 'prophet' doesn't speak as God speaks but out of their own heart or from what the masses think. Even Peter was a victim of this when he refuse to eat with the Gentiles. The difference though he repented they did not and the polluted message goes on today.