I recall a few characters last year during the 5K portion of the event.
I believe just inside the entrance to the park, going up the left trail (from entering the park) just past the restrooms/locker area, I believe there were King Louie and Baloo (I don't recall 100%, but I know there were two of them at that spot, with Baloo being one of them). I believe they were available for pictures.
Also, when running up the Rafiki Planet Watch-area roads, Minnie and Mickey were up on that bus, but you could not stop and pose with them for a picture, obviously.
But, those are the only four characters I remember during the actual race/scavenger portion of the event.