At the above link, two non federally recognized tribes are selling memberships in their tribe to illegals as a way to avoid being deported. While the cases are probably just a scam, they do raise interesting possibilities.
For instance, being a member of a tribe is a political decision, not a racial one. Because the US Supreme Court has determined that the tribes are "quasi-sovereign" (like quasi-virgin maybe?) they can decide who is a member and who is not. It is not based on a blood quantum, unless the tribe decides that is the minimum standard. However, with each succeeding generation, the quantum will be reduced, to the point that it will not be sustainable as a measure of "Indianess."
By selling memberships, tribes will be able to increase their population, and possibly increase their claim to federal benefits. This is really quite fascinating in a way.