Yes, solid-state relays can switch AC.
Bollocks: if you really need that kind of alarm, then your setup is wrong. Trust the relay, or use a solid-state one, then wire up a LED to let you know that the pump gets AC.
The real problem is when there is no flow, because your pump could still be getting AC, but still be fried, so what you do is put a flow sensor: that way, you're looking out for the actual problem situation.
A flow sensor will tell you if:
-a leak occured and the system is out of coolant
-the pump has stopped working
-the system is obstructed
If you think about it, your system will always run fine, as long as any coolant is flowing.
