Moving this over to the Disney/Pixar forum, since that's really where it belongs.
Haven't seen the video (no Flash on the browser during the day), but I think the cameo in Cars is real. I remember someone somewhere pointing out that WALL-E was in the movie. The Incredibles cameo is possible, but not very likely, since I don't think they had started on WALL-E that early. The cameo in the first Toy Story is highly implausible, since the first trailer mentions that they didn't even come up with the idea for WALL-E until after Toy Story was wrapping up.
It's not the first time they've looked ahead. Nemo shows up quickly as a stuffed toy in Monsters Inc, which came out 2 years earlier.
-- Ed