Basically has to be a reasonable interpretation of a character they have the rights to. It's a very broad standard, and the burden would be on Disney to prove Uni's interpretation is not true to the character. As long as Iron Man wears red and gold armor with a red light in the middle and fights bad guys, would be fine.
[Endgame spoiler incoming]
In other words, Disney has no veto to say "we don't want to make
movies anymore, make a Venom ride instead. Uni can really do whatever they want as long as the characters stay true to the source material. Just remember, MSHI is overbuilt by modern theme park standards, with three E-tickets and a C-ticket. I'm sure they see no need for a fifth ride.