The current sensor switch may or may not work. I have one of these on my dryer that automatically activates a dryer booster fan when the dryer is on. It works well in that when the dryer is on, but not running (ie: you are setting the temp/time, etc), it does not activate the fan. This is how you would want this to work with the variable speed pump so that when the pump's control panel was on but the pump was not spinning the switch would not activate. I don't think the current switches are intended for this use so not sure if the current is enough to not run the SWG when it is not only just on but not spinning but on and spinning but spinning too slowly. If you go this route, look for an adjustable current switch.
I think the best solution is to get a variable speed pump that has builtin protection for a SWG in the form of a relay that controls the SWG power based on both the pump being on and being at a proper speed. Either that or automate.