Obviously not exclusively, in the same way Quicksilver & the Scarlet Witch were part of the X-Men contract but can also be used in the Avengers movies. I wonder if either Fox or Marvel could make a Silver Surfer movie, since both companies probably have a claim to the character...unless exclusivity is spelled out in the contract. Contracts are weird. Especially contracts written by a company in bankruptcy and desperate for money at a time when superhero movies are anathema. Obviously, Marvel wishes they could turn back time on the X-Men, FF, and Spidey contracts. Or at least shoot the grandfathers of the long-gone executives who signed them, cashed their severance checks, and moved on to bigger things.