I actually agree with Hayworth that he should feel under no obligation to return donations from the tribes, and I agree with many of the stances he has taken supporting them, especially with regard to the case of Cobell v. Norton. This is a case that has been going on since 1996 (with underlying issues going back to the 19th century), when Elouise Cobell of the Blackfeet Nation of Montana filed a federal lawsuit to get a proper accounting of what the Department of Interior (DOI) has been doing with funds collected from leases of land held in trust for American Indians. In the course of the lawsuit, it has been found that the DOI intentionally destroyed records (and allowed others to be destroyed by the elements) and covered it up, did not maintain records with proper security (which led to DOI websites being removed from the Internet as a result of an injunction).
On the other hand, Hayworth has held multiple fundraisers in sports stadium skyboxes owned by Abramoff, the value of which he failed to report to the Federal Election Commission, for which he refunded money to two tribes and filed amended FEC reports. If specific evidence of other failings along these lines--or of actual bribe-taking--is found, Hayworth should be nailed to the wall. The fact that he has had extensive involvement with Abramoff is itself reason to scrutinize his dealings carefully, as it's a sign that he is either a poor judge of character or doesn't care about who he associates with (it could be either, since he isn't the sharpest blade in the drawer and is one of the biggest blowhards in Congress).
When Hayworth first ran for Congress, he signed up for a dialup account at Primenet, the Arizona ISP where I worked at the time. His campaign manager said that if he won the election, he would be sure to remain a Primenet customer for quite some time. Shortly after his election, the account was cancelled.