As was stated earlier, the hot water valve will not prevent from getting water, but will prevent you from getting hot water. Some water will still get through to the hot water tank, but with the middle valve in the open position cold will mix with hot and thus feels like you are getting very little hot water.
I agree with RSchleder...given the dealer still had you in winterize mode i would not be surprised if the valve by the pump to suck water from tank vs RV antifreeze jug is likely in the wrong position, which is not allowing you to draw from the tank...first thing you need to do is let us know if you are getting any water at all, from any source with the pump...the water heater valve will not prevent you from getting any water.
But again...your husband is correct...
, the water heater needs to be full prior to operation, or you risk burniong out the element.
BTW...there many dealers just like yours, hard to imagine but the industry is riddled with them.