First dollar deals are nothing new in Hollywood at all, though the one mentioned seems a little overly generous to be believable. Ron Howard is rumored to have picked up $15 million and Russell Crow was supposed to be somewhat less than $20 million. Since Ron Howards company is producing the movie they would get a share in the revenue, but its the same deal Disney has with Bruckheimer, Spyglass, Icon or any other outside production company. No one at Disney would actually do anything to make the movie; the real work (building sets, renting cameras, sewing costumes, etc.) would be done by Imagine. They would obviously get a cut of the money.
Then again, they were tremendously eager to get Ron Howard on the project. He was signed when it looked like Bruckheimer was bolting the company and Disney desperately needed a name to work with just for appearances sake. I wouldnt be surprised if someone offered the moon just to get certain people to commit to the project, and then those same people turn around and welch on the deal.