It looks like the opening where a flashing blue strobe light, spotlight or other emergency accessory would be mounted. The hole just looks too clean.
Yes, and notice how the hole appears right in the middle of the 'red cross' as though that were used as target acquisition. Any munition making that size of entry hole would have incinerated that ambulance. This would be laughable if the stakes weren't so high.
What I find so amazing, is that now Reuters and AP among others have egg on their face presenting obviously faked pics, and the Today show brings us this pic that has the earmarks of propaganda all over it. The hole is right in the middle of the Red Cross! They aren't even putting forth any effort!
Not only that, look at the ring of unpainted metal around the hole! That's where whatever was there was fastened to the roof before the vehicle was painted. I'll be it you could get a clear enough look at the perimeter you would see the holes where the object was fastened to the vehicle.
It is probably an old ambulance that they retired and the guy who bought it took off the light and didn't bother to paint it. Around here they sell old police cars and people often drive them around as is w/o the police insignia and lights but they still look like police cars.