Peanuts, by Charles Schulz, especially in the later years had a running joke about Spike having Mickey Mouse shoes:
Another strip says that they were given to him by Mickey Mouse, but I can't find it.
That said, it got me wondering: Peanuts, being a one man show, could acknowledge other universes (There's even a strip where Sally writes to Harry Potter). However, does Mickey ever reciprocate? Is there any time where Mickey mentions a cartoon or comic character not owned by Disney? (Preferably Peanuts, but any cartoon/comic would count.)