Each company is different I guess. I don't think the OP said it was a hit and run. I think Benwrigh inferred it was a hit and run though.
I'm only aware of Allstate in Florida charging it as an at-fault if its an unknown vehicle. So it sounds similar to what Benwrigh was inferring.
The OP definitely inferred it was a hit and run. He did this when he asked "What would a hit and run be considered", though never clearly stating this was a hit and run.....
Now, what do you mean by 'unknown vehicle'? The hittee or the hittor? I'm not clear on this. I'm just curious, always interesting to see different state rules on some of these common situations.
Dan