You can heat a tub with electricity, but it must have a good cover, and it sure doesn't hurt to insulate any plumbing which is above ground. Also, fencing in the equipment area to keep the wind off of things is a good idea. Expect to pay a lot of money on power.
If your friend doesn't want to do the cover/insulation thing, have him check into gas heating - but be aware that the pump must be running for the heater to work, so it is really heating with gas AND elect.