how does what happened inside Bruce's mind transfer over to the Astral plane?
at least with a regular Hulk you know that he's got all sorts of super-natural powers (seeing/grabbing ghosts etc) but "Devil Hulk" is not even real, in the sense that he's not manifested in the world outside of Banner's head ...
i am sorrry but it may be big and fightenning for banner but for xavier it is only someone elses problem. thus metaphysically he would end up been nothing xavier cant handle as it has no power over xavier ( in the same way nightmare has no power over the sleepwalkers) i mean i would say that shadowking is alot more powerfull then this devil hulk charcter