The only I can really think of is Cephalic Carnage...at least i think that dudes native american..

if there are bands whose subject matter involves native american culture, it'd be even better

Chuck Billy of the thrash metal band Testament is Native American.

Aaron Carey from Angelrust is Native American (although he is also Irish and looks very European), although the band doesn't talk about Native American Culture.

Resistant Culture may have Native American members but they surely talk about and incorporate some Native American influences through lyrics and music. Tribal grindcore!

Blackie Lawless?!

Isn't the lead singer of Immolation a bit Native American?

And I think Lenzig from Cephalic is hispanic.

Blood of the Black Owl; I don't know about Chet's genetic makeup, but his music is very native PNW influenced.