I agree that if the ethnic group in question is still around, you should be super-careful not to step on toes WRT burial sites.
But, for example, there have been NO ethnic Ancient Egyptians since the early Muslims essentially wiped them out. King Tut has NO descendants to complain about his post-exhumation treatment, really.
As long as you're respectful in treatment of the remains (I'm thinking of idiot Victorians who had mummy-unwrapping parties for kicks, and that sort of thing), remains from peoples without descendants can and should be examined without any real issues.
And if the descendants ARE still around, I'd say take small samples, X-rays, and other things that can be done without causing major damage, and once you've got small amounts of "dead guy" to experiment on, sure, why not let them re-bury the body? Science benefits, the people feel connected to their ancestors, everybody wins!