OK, I actually checked, the autopilot servo should be back-driving the wheel, and since the SECU is using wheel position to drive the spoilerons that means that the autopilot does have indirect control of the spoilerons. So my guess that maybe the autopilot servo was an aileron only device was wrong. Cap'n marvellous is right and the spoileron-to-aileron gearing should be identical whether AP is on or not (although in practice, being driven from a different point in the circuit there will be small differences, but you'd not see them I think).
So I'm confused who Genghis saw one device only move, unless it was the flight spoiler, but then why would the a/c roll?