Hasan was only marginally associated with some panel that was discussing terrorism, but he does appear on videos of the meetings as an audience member and did have to get at least minimum security approval to be admitted (attendees had to sign up in advance). The Israeli ambassador also attended many of these meetings, and I have read suggestions that perhaps Hasan was trying to come up with some way of assassinating the ambassador.
I don’t think that he and Obama knew each other personally or that Hasan was really part of the “transition team,” as that is generally understood. However, it would be interesting to know if his name shows up on the WH visitors log...
No, it wasn't the official transition team, just one of the many think tanks trying to make themselves relevant to the new administration.
It's more likely Hasan was shuffled off to the conference by his supervisors at Walter Reed, since he was generally a waste as a doctor -- being described as "lazy," "neglectful" and "unfriendly" in addition to his habit of spouting militant Islamic tirades.
He may have been pushed out to quite a few conferences, just to get him out of the way.