Originally Posted by metaphysician
Why wouldn't they be able to?
If Fox have rights to certain visual representations of the character and Marvel have other visual representations, then they might be limited. Or maybe one only has the essence of the character but can't make it look like the classic image at all.
Viper in The Wolverine was somewhat similar. She wasn't the Madame Hydra look but reimagined as some kind of mutant who could shed her skin and has a long tongue. Also she has blonde hair instead of the familiar dark green.