I don't think so. A little trap, a little side, a little rear?
Much of that depends on the grip you take and the level/height to which you pull the bar.
Narrower hand spacing will activate more traps, while hands further apart will target more shoulders.
I will say that i feel db's are more effective than a bb.
Did you check out the video Bench posted of Jay Cutler training shoulders?
Observe his "technique" on lateral raises - specifically the topmost portion of the concentric part of the rep.
That is almost identical to the position I end up in when doing uprights.
Done this way, I feel the most delt stimulation.
I never thought of using db's in lieu, while combining them with a bit of a lateral raise-type motion.
Seems interesting, and I may give it a go next week.