Water pump as air pump or vacuum pump

Circulator pumps can be used in open loop systems (though I think these are typically aluminum or brass rather than cast iron since the latter will corrode in an open loop system).

There is no way to know if your particular pump will suffice because we don't know the head loss of the hoses or the heat exchanger. I'm assuming the 13 M^3/hr figure is pumping against no head. You will of course flow less the more back pressure involved. You also have not said what flow you actually need. If you know the model number of the Grundfos, it should be a simple matter to download the pump curve. That will tell you the flow at various head pressures.

You could measure the head loss of the heat exchanger by putting pressure gauges on the input and output of the exchanger. The difference is the head loss. Bear in mind, however, that the head loss will depend on flow rate.

Probably the easiest thing to do is just connect the pump as you envision and see if you get enough flow.

Use a siphon. Get decent garden hose (that won't collapse if you draw a mild vacuum) and that's flexible enough to stay in the bottom of the pool area.

Run it from the center of the "puddle" to a point a couple feet below it in altitude, e.g. That storm drain.

From this bottom point, prime the siphon by sucking all the air out of the the garden hose. At this point, water will siphon continuously until the puddle is drained or the high end of the hose goes above water.

Once air gets into it, you'll hear a slurping sound, which means you lost the prime. Fix why that happened, and re-prime.

A shop-vac is an excellent way to suck on it. If you did it with your mouth, you'd be tempted to raise it up to your face, and that end must be below the intake end.

The greater the height differential, the faster the flow. The higher the peak is from the inlet, the more difficult it will be to prime.