What kind of boiler heat exchanger do you have? O2 in your circulating water can kill lots of things, not only pumps. If there is a risk of say power outages, or you want to shut the system down, you can add antifreeze to the circulating water...you may need to run it a little warmer, as the antifreeze decreases the heat transfer. With the tubing embedded in concrete, you may not get much O2 migration - it is the exposed areas that would be the bigger concern.
Not sure about the longevity, or the best approach. See what other comments you may get.