Primary roll control is with the stab, with additional roll augmentation from spoilers on the wing..it's always an eye opener for the uninitiated to watch a flight control check on the ground, and see the stab go full up, full down, then split with one side up and one side down.
Yep, the ground crew confirms stab position during preflight. Sadly, the RAIDER 21 incident at Andersen showed how important stab trim position is on the BUFF. https://usaf.aib.law.af.mil/B-52H_Andersen_21Jul08.pdf