I think the natives knew God. They called him "The Great Spirit". They maybe didn't understand everything at first, but it's possible that perhaps the spanish were able to find America to bring the bible over. Of course there was a lot of bloodshed by a lot of evil men over the years, but if one single soul was saved as a result then it was all worth it. I believe a lot of cultures believed in Monotheism, 1 God who created everything.