A Representative for AMD stated in an email that the Wii U uses a specialized AMD E6760 GPU. Whether this is legit or not remains to be seen but the email where the rep makes this comment appears to be legit.
Did the rep just make that up? Or is he/she telling the truth?
UPDATE: AMD's head of Product PR Phil Hughes just responded to Gimme Gimme Games on this matter. Hughes doesn't deny it, only saying "We can confirm that the Wii U will use AMD graphics but we have not provided any specifics on what silicon they will be using in the upcoming console."