I don't think it's justified on Disney's part even if they have their own "Santa." If they allow anyone to enter the park dressed in holiday clothing, they have no right to deny this man the same right, just because he looks like Santa. There are people who look like Elvis, for example, and may play up on that and people may ask for their pictures with him. As long as he's not charging and people are using their own cameras to get pictures, I don't see how Disney has any right to interfere. If it is because he is dressed like Santa, then no one else should be allowed to dress up either but according to him others are allowed to.

No reasoning would make me see how what Disney did was justified. If he had set up some kind of booth with a professional photographer and started charging, then I could see it.