[acidrain]

Well, we've had the lead vs. aluminum cathode debate before, so let's not go there...
I used those pumps quite a bit when I first started out. They are typically ceramic shafts, so are safe in acid. The problem will come after a couple months in the acid... the plastic will become brittle, and crack at the impeller. For sure it will go out right when you need it the most, so either have a spare on hand, or go with a HC (high corrosive) rated little giant. I picked up a monster (220v) HC Little Giant for ~$50 on ebay.
Why don't you go the other direction? Use chilled clean water inside pipes ran in the acid tank. That would keep down the apparatus placed inside the tank.
As long as you use metal pipe as the heat exchanger, I think it would work fine.
BTW, This is how I heat my tank (with PVC as shown). It just wont work with cooling (with PVC).
Got any friends with TIG or MIG welders?