How would you pull it off with that one reservation that's split between the Dakotas? Or the big one in three of the four corners?
The one in the Dakotas is one county in ND and SD.
He's probably referring to the triangle shaped one (Lake Traverse). In that case, it really doesn't matter because basically no one lives in the ND part of it, and almost everyone of the very sparse number who who does is white (of course, even the SD part of it is majority white).
Might not be a bad idea if there was a size requirement. All of those really tiny ones would create obvious problems.