Probably.
The bilge pump is probably a centrifugal pump. These pumps have vane that spins and pushes the water up and out the hose. So long as there is water, the pump works great. However, these pumps don't pump air. When the float switch bottoms out, the pump stops and any water in the hose flows back down into the bilge. There is not good cure for this characteristic, save keeping the hose run short. If a little water in the bilge is an issue use a sponge to dry up the residual water.
A diaphragm pump will suck and push water and air. These pumps do not have the back flow issue.
Also read the specs for the pump carefully. The pump will pump 950 gph if there is no head and if the it supplied with charging voltage, i.e, about 14v. In real life the out put is much lower. It is all marketing.
Two answers.
A check valve, which will reduce flow a little and can clog. Also, if the boat is left in the water in cold weather, a check valve can lead to freezing, followed by sinking (the check valve prevents the line from clearing, allowing the line to freeze between cycles, which can be hours or days).
Not that diaphragm pumps have integral check valves and all of the weaknesses associated with them.
Run the hose up as high as possible as soon as possible, and then down hill to the thru-hull. This will reduce the flow back.
I'm not sure if advertising pumps at zero discharge head is bad marketing or weak (which is understandable) consumer understanding. They should put the pump output curve on the box, although I'm not sure people would understand the effects of plumbing or what discharge head means.
