I don't know, that's just what I've heard. The way I see it is that the alternator is always turning, the regulator just controls what it is putting out. The main idea is that not having a belt/mechanically driven pump means 1 less item creating friction. Not that I believe the pump puts that much drag on the engine, the difference is very little, if at all. The main advantage to using a hydro-electric pump would be that there would be no need to find/buy a dual groove crank pulley and no need to fabricate brackets to mount a belt driven pump to the engine.
