Yes, if the truck shop uses the righ electic pump, it will dump fine. Just to ease your worries.
All my F 350-F 550 dumps are electric hydro pumps. I also have 1 F 650, with a low profile body, that uses an electric pump, and it will dump a full load of rock. However a full load of rock, on the F 650 was a little bit more than the pump wanted to do, but the pump did the work. Never had a problem with the Dump bodies on F 350s - F 550s, have hauled full loads or rock, sand, and loam.
Don't worry the electric pump will be fine.
Geoff