I think this would be a nice addition! Maybe he can move to the farm cave!
Dang it. I just thought of this idea, and I was going to post it.
Anyway, if this is done, I think it would destroy whatever is currently in the cave, but maybe the dwarf would give you some ore every day instead? Maybe there should also be a direct tunnel to the mine from the cave, not that you need another one. Also, since the dwarf isn't in the house, I feel like this would mean you could have both the dwarf roommate, and still be able to marry.