Hi there! You can absolutely have the shadows unable to swallow Vincent and their hold just won't take. They won't be able to harm or control Vincent whatsoever.

That being said, if you wanted to play with the idea of the shadowkin recognizing Vincent's darkness and thinking that he is one of them (or at least partially like them) you can play with that too. The shadowkin might even be jealous that Vincent has his own body and face to use.

Hope that works!