Speaking of Gex, someone on NeoGAF found this on IMDB. I have no idea how IMDB gets their information, or if they're even reliable, but here it is. I'm taking it for a grain of salt right now, but hey, it's fun to speculate.
Playstation All-Stars Battle Royale (2012) (VG) - Full cast and crew
If it's true, Crash, Spyro, Gex, and Rayman are in (along with the obvious ones like Jak, Ratchet, and Cole). Keep in mind that if it's true, not all of the characters listed may be playable. Bentley's already been seen in the game, but he's part of Sly's level 3 super, and Qwark is part of the Ratchet and Clank stage.
It seems to be in line with a recent interview with the director of the game though.
PlayStation All-Stars Battle Royale Director talks roster selection and more in this interview
He says in that interview that they listened to the fans when it came to characters, and they haven't had any issues getting third party characters. Crash and Spyro I would assume would be the first two third party characters they'd try to get in, and if they were among the first third party characters, and they haven't had any issues with third parties yet, then they both may actually be in.