Well I am also no AC expert. Infact, no experiance at all, so I am ready to step aside when the experts step in.
But I do know pumps. I am presuming you must be useing a centrifugal pump. They are high volume pumps and can be high pressure. Just depends on the design need. However, they will lose pumping ability as soon as air is introduced and if cavitation is seriuose enough. They rely on the inertia of the water flow to maintain lift
. It seems a little strange that this type of pump is mounted above waterline. It must be a real hassle, as the slightest little air leak into the system (often around the shaft gland) would mean priming again. I would have suggested that the pump is below water line. But as I said, I know nothing about the AC stuff, so I guess there must be a reason why the pump is not.
As for scoops, when staionary, no the scoop will not aid the pump. As I said before, if anything, it can be detrimental. Any restriction to water flow and ingress could cause cavitation. The bigger the inlet the better is the idea, but of course on a boat, that isn't praticle and the the biggest skin fitting you can get away with is what will be required. The less restriction, via either inlet diameter and/or length, the better the flow of water into the pump, thus the bigger volume of water out of the pump.
A scoop may help when under way, but it needs to be big to aid giving the inlet any positive pressure. Most off shelf scoops I have seen are simply not such. The only scoop I would consider is the AC manufcaturers recomended one, if one is made and is practicable to fit.