The biggest concern isn't running the engine, it's the ice freezing and expanding and causing things to crack.
If you are concerned about it being frozen, start it up and let it run for 10 minutes and shut it off for 15 minutes and then repeat that process a couple times until you know you have warmed up the engine enough to melt any ice in it. You don't want to overheat the engine because the coolant isn't circulating. Now, if you get the engine up to operating temp and you still have no heat, that could mean it was frozen and the heater core still is. That's when you get it into a heated building ASAP before it gets any colder and bursts the heater core. If you see and leaks after running, that's a good indication it was frozen also.
Thursday, January 1st, 2015 AT 3:12 PM