Which rights? I've not heard any substantiated rumors (let alone facts) about Viacom being involved at all. Someone has CD/DVD distribution, and has since year one. But no, neither MTV nor Clear Channel have anything to do with Bonnaroo.
I think all those bonnaroo rumors are just created by jealousy, because it's been so successful, without major media presence. they definitely have some sponsors, I suppose. but not the ones purported (like MTV). Hopefully it will continue without all the commercial hype. about shakedown fest, I'm still shaken by that (no pun intended). very sad situation.