A scupper is scoop-type thu-hull, instead of the basic mushroom-type. If you fill while moving and use a large diameter thru-hull, seems like they would both prime easily because of the pressure from the scoop. You will need valves on both pumps anyway, so if you only want to use one pump, you would have the other pump's valve off so no air would be sucked through it.
Seems like testing this would only cost you a T fitting, and you could always put in another thru-hull and pump if you didn't like the performance.? And like Rod said, keep the pumps as low as possible.
Or buy Simers.