My system goes:
VP -> Check valve -> Vacuum switch -> Vacuum reservoir and various loads
When the VP shuts off, it will "bounce" quickly three or four times, I can hear the relay click and the VP actuates very briefly. Can't be good for the relay or the VP, and I'm confident that a vacuum switch with turn-on and turn-off points separated by at least a small amount would fix this.
Here's the relay I went with:
http://www.pickercomponents.com/pdf/Relays/PC795-80-Amp-NO-60-Amp-NC-240-Amp-Switching-Mini-125C-Automotive-Relay.pdf