Ruthie,
Sorry I have no idea about which characters are included in that appearance. And I can't recall if others have reported that in the past. However, given that several characters make an appearance at the Mickey's Backyard BBQ meal, I think you would be assured of more than just Chip & Dale coming over from the campfire.
Sounds like you have a nice day planned. HDDR, relax, characters, then you can stay if you wish for the golf cart parade, trick-or-treating, and campfire-singalong-movie. The Friday forecast looks good.
Let us know if you get your picture with Pluto (I'm a Goofy fan myself).
Bama Ed