What source are you talking about? All I see is a bunch of left-wing blogs discussing possibilities and theories. That hardly constitutes proof of violating tax law. I live in Alaska, remember? If there was an issue of tax evasion it'd be news up here.
Here -- I can use your research methods to prove things, too!
Besides, your expressed concern on this issue is downright ridiculous considering the Dem's readiness to blow of documented tax cheating by the Treasury Secretary.