Almost every Marvel super has been on an Avenger team in their life; it's like Marvel jury duty.
If a short-term stint in an Avenger title excluded that character from WDW according to the Uni contract, then no super would ever be allowed in WDW. But, the original contract envisioned that there would be many other characters. So, being part of "Avengers family" could not have been construed broadly enough to exclude all characters, but an more intimate relation is presumed.
Also part of the original contract is a use-or-lose clause. Uni once had the opportunity to grab literally hundreds and hundreds of characters for their parks, but stuck with the handful of "families" it originally chose. And so, they can't lay claim to more characters than what has already appeared in their parks unless that character is very closely tied to one in use.
On top of that, we've been told that there was an updated contract which was more specific about what can and can't be used by WDW, and we don't know the contents of that. So... we can't be sure of anything until that character appears in WDW. And so far, GotG and Doctor Strange has appeared in WDW. And that's about all we know about what can be done around the fringes of The Avengers.