I've never seen "Aguirre," so I'm not so certain of how that worked but enslaved Africans played a significant role in the Spanish conquest of the Americans. An African slave named Esteban was part of the disastrous Cabeza Da Vaca expedition to Florida and was one of only three survivors. He served as an intermediary between the two Spanish conquistadors and the indigenous people and engaged in various mystical displays that earned him reverence from the native people and a quasi-religious following. Another person I know who was in a similar situation was Jan Rodrigues who was a free afro-hispanic voyager from the Dominican Republic who was an intermediary between Dutch traders and the Lenape of what became New York City. In fact, he did so well with the indigenous people that he settled amongst them, making him in the eyes of some historians the first non-indigenous person to reside in Manhattan. I hope that answers your question.

Sources: Crossing the Continent by Robert Goodwin (the whole book is about Esteban) and Gotham by Edwin G. Burrows and Mike Wallace P.19