I dunno, my 3 year old knows a lot of characters that he's never seen on tv. For example, he's fascinated by Batman, Spiderman, and any superhero looking character he sees in a store, a book, poster, toy, clothing, whatever, but of course I would never let him watch those movies! He asks who they are and I explain. So I wouldn't stress if he asks and then knows who Mickey is or whatever. If he wants mouse ears, so what? You can buy them or not, y/k? Maybe I"m not understanding,but I don't see the harm.
We haven't been to Disney yet but we went to Six Flags, and DS was full of questions and stories about Scary Bunny (Bugs Bunny) and That Loud Man (Yosemite Sam) but he didn't ask us to buy any of the junk. Other than park food, lol.