If they are on sovereign land they can do what they want...
Living in Arizona, it has quickly become apparent that Indians can claim ANY LAND as theirs. There was a big kerfuffle a while back about an Indian Casino being planned within a block of a high school. Cannot remember exactly where in this area, but the Indians won their suit. Political correctness affords the Indians pretty much anything they want. Some of the Indian Casinos are nice, some are dumps. But they always generate revenue for the tribes.