Turning on the heater is an old-school trick that will cool your water temp down on the dyno or the staging lanes. You are correct that it will act as an additional radiator of sorts.

WRT to the A/C, that's another can of worms. IMO, the best application I've seen for A/C utilization is this one:

http://www.killerchiller.com/

I'm looking into it for my E55 AMG, but it would work on any FI car with an air-to-water intercooler setup.