Yeah, pretty much any chance to trade a TE not named Gronk or Graham for a potential top 10 RB I would jump all over that.
*edit: Now I'm not saying that Manning doesn't turn Thomas into one of those top flight TE's by the end of the season. The thing is, unless you are playing against the guy who has Graham or a healthy Gronk, Gates will match up evenly with almost every other TE out there. So you aren't losing much of an advantage at that position while gaining a huge one at RB by locking up a second potential top-10 guy at a key position that lacks depth this year.
(Based on your "is there any reason I shouldn't jump on this" comment I'm sure you already realize this. I just like to explain my reasoning so perhaps the less experienced people following this thread can see where I'm coming from.)