I hadn't thought about the moment being applied to the mast through the flapping hinges - I didn't realize that the fully articulated system is always acting on the mast though it makes sense to me now that Induced Drag mentions it. I had asked an Apache pilot who has quite a bit of NOE flying in his background and he said he had never noticed a rolling tendency. I image the rate of roll would be damped somewhat by the mass of the helicopter, and the Apache is not a particularly light bird. Perhaps that combined with the lateral controllability even at negative g makes it a non issue.
Thank you all for the information!