Yes as long as the pump volute is full of liquid, you can close the valve on the outlet side of the pump to zero opening without any damage. The load on the motor will actually decrease as the valve is closed and the flow decreases. You will be able to hear the motor speed up as you close the valve and the motor load decreases.
I have found that its a good idea to keep the motor running throughout the time that I'm recirculating my wort with my March pump since the impellor can seize to the shaft due to sugar buildup. I just close the output valve as needed and the impellor never has the chance to seize. Once I've performed the wort runoff and sparge, then the concentration of sugar in the pumped wort goes down and the chance of seizure goes away too.