Quoted from Rarehero:

There's no reason they wouldn't. Animation is much different than live action. Not only should they be able to get all existing animation, but probably also CG assets to create anything custom that they need. Tom Hanks' bro can do custom Woody voices...and it would be great to get some other custom voices as well, even if they're sound-alikes. Don Rickles is gone, but a sound alike for Mr. Potato Head to insult you as you play would be really funny.
Sometimes it's not about payment...it's about there being layers of loopholes, production companies, agents, etc that almost make it impossible. Pirates is a Disney movie, but produced by Jerry Bruckheimer Productions...it was probably just a huge convoluted mess to figure out rights issues for everything.