I can't imagine paying for "Pixie Dust" at Disneyland or Disney World. It just doesn't seem like a Mickey-endorsed thing to do! If the last 20 years' worth of check-in CMs are an indicator - I would say that it is NOT a good idea to tip them. They probably would assume you had a $20 bill stuck behind your license, and promptly hand it back to you! Nope - not at Disney!