Pikkis
Prince
Well, for the Sioux, they weren't really a civ; they were nomadic and had no writing, etc. I think the Iroquois are more likely.
Still the only Native American leader in BTS was a Hunkpapa Lakota Sioux war chief, so I think the Sioux are possible. Also, the Mongols were nomadic too. Anyway, you're right in that Iroquois deserve to be in the game or in one of its expansions, so I added them to my expansion list (though 14 civs makes it probably too big an expansion to be made).