Jmr40 really summed it up. All things being equal, the shorter barrel will vibrate less because it's stiffer. That, in theory, means the shorter barrel will be more accurate.
This is really getting into symantecs, but to be accurate, consistency is necessary. You could probably even say consistency is accuracy. for your original question you said all things being equal so we have to work off the idea that everything is happening with perfect consistency.
For spotter vs bull, I would have to assume the bull barrel is theoretically capable of better accuracy, but I've heard arguments both ways. I know in real world, sporter barrels can be made accurate enough that factors such as the marksmans ability, can be a bigger difference than the difference of if the barrel is sporter or bull weight.