It makes it imperative that the source of Indian identity be clarified. There is a very intelligent and sensitive article on this topic by Joseph Marshall III in On Behalf of the Wolf and the First Peoples . Enrollment was imposed upon the tribes as a part of the allotment process. Perhaps the most famous such occurence was the Oklahoma Land Rush. Tribal membership can be a very touchy subject.
Different tribes can and do have very different policies.
Some welcome members with open arms. Others guard their membership rolls carefully. After all, this is a phenomenon seen commonly in all societies. In times of plenty we are all willing to share for the public welfare. When money gets tight, the knives come out, be it in academia or on the street.