The thing that bugs me the most about Hogan signing with TNA is that I just don't see Hogan in an authority role. His character has always been the American hero standing up for what's right and somewhere down the line, he would just have to get involved in the action in some capacity. The non-wrestling role for Mick Foley worked because he had a previous stint as WWE commissionner and he had credibiility so it worked. So to me, it's crystal clear that Hogan looks to wrestle actively in the promotion, when his body will allow him to.
In itself, TNA made the best move to ensure themselves the #2 spot in wrestling because this brings them immediately to the next level with WWE. However, we pretty much don't know what are Hogan and Bischoff's hidden agendas (maybe there isn't any hidden agenda for Eric Bischoff since I can see his expertise in TV production being put to good use to help TNA upgrade their own TV production) but I honestly don't expect Hogan to sit quiet and not complain if something doesn't go his way. Hogan's at this stage of his career where he'll need to pass the torch to the younger stars like Kurt Angle and Sting has done with TNA. With Hogan's track record, I'm 100% sure this won't happen.