When legal/financial effects are the result of a vague definition of dividing of humanity into ethnicity/heritage there will be social upset. If there was a genetic test to establish absolutely tribal membership, would that become the accepted rule? ("Sorry, you carry only 17 out of the established 37 markers, you're out") It seems unlikely. Membership via genetics or 'appearance' is asking for trouble whether to define whose in or whose out.

do the feds have any muscle in this case?

The feds have no say. Its the Tribes right to determine their own membership. Do we really want the federal government to force the tribes to do something?

Basically Indian tribes are breading themselves out unless they only have relationships within the tribe. So as more people leave the tribe that casino money gets split by less people. This is a race issue, and a greed issue.