Now, Voldemort's a strong Legilimens and Occlumens. Wouldn't he be able to block out the Imperius? See, all of the Unforgivables mess with the mind. Imperius controls, Cruciatus tortures, and Avada Kedavra shuts off all body functions, I think...?
Is that the way it would work? And if so, then wouldn't he be able to resist Imperius? Even from Dumbledore? I don't know if there's anything in the books about his mental strength, just that he can control people and their minds, but not anything that he can do for himself. As far as I can recall, haha.