Not being familiar with that system, I am going to go out on a limb and say yes you are correct. Typically, the circ pump is told to run when there is a call for heat. When the circ pump starts and creates some water pressure, a flow switch or pressure switch will trip and turn on the heater. The other function of the circ pump is, of course, filtration. It will also run to accomplish filtration cycles. Your spa may have adjustable filtration cycles that will cause the circ pump to run longer or shorter, or start and stop more often.