Sorry if this has already been asked, but doesn't this fall into the Marvel characters can't appear at WDW because of the old deal with Universal?
Universal does not have exclusive rights to all the Marvel characters, they only have the rights to the ones they are currently using, or ones that are in the same family. So for example Big Hero Six has no connection to other Marvel characters (at least not that I know of), so Disney can, and has, used those characters at WDW. On the other hand, Iron Man is clearly part of the Avengers and since Uni is using Hulk and Captain America, Iron Man is off limits to WDW. GotG is in the middle. In the comics GotG characters do have some connections to characters that Uni is using and it's further complicated by the fact that there are two different incarnations of GoTG in the comics.