Not a lawyer, but I'm assuming anyone who's mentioned in the Hobbit, the trilogy and the annexes (ie the stuff Amazon bought the rights to) even in passing can

Not a lawyer, but I'm assuming anyone who's mentioned in the Hobbit, the trilogy and the annexes (ie the stuff Amazon bought the rights to) even in passing can make an appearance. However, if these people do things exclusively described elsewhere in the way they are described in those other works, there's an issue...