I think Vita used that and maybe still does along with the heater. I saw it on the circ pump I believe, the idea being your heating the water while drawing heat away from the pump.
I guess it works as long as the heat transfer can be made (metal to metal) efficiently - it would be essentially a water cooled motor. The only problem could be it could heat the water too much as what happens to water temps in the summer with the other pumps running.