I used to live in Maine, near a golf course. I can tell you that every spring the maintenance crew had to go around fixing underground sprinkler piping and the heads that had been blown out the previous fall and yet still froze over the winter. Blowing out the pipes doesn't get all the water out of them. It gets most of it out. It can still collect in low spots and freeze, causing the pipes to burst, split, or break joints.
In some cases, water can leak back into the system through puddling at the heads during a winter rainstorm/early thaw and refreeze. It may not be worth the effort and expense to install underground sprinklers in his area if this will happen. I suggest you check with a neighbor or the local golf course and see what their installaiton and experiences have shown.
Heck, I live in south Florida (no freezing here), but keeping the head on the pipes around here is the most annoying part of the underground system. If anyone trips or kicks one, a car or lawn tractor runs over one, they usually pop right off their plastic threads and then you have a fountain... ;-)