For the Native civs I've found themes for so far, I've tried to take music from actual Native artists and not non-Natives. Either way, any music that has the appropriate style for the mod is going to be stereotypical and inauthentic. But in my opinion a Native artist is better than some European-descended white guy who makes a living composing stereotypical "ethnic music."
This musician is half Seminole: https://www.youtube.com/watch?v=XABJsEzsz8E
By the way, in the future can we discuss minor specifics like this on the document itself so we're not flooding the forum with them? I know, I may have started it.