I've used Hammer a bit before, and to my knowledge it wouldn't work that way. From what I'd expect, Source Engine maps aren't stored or treated as models, and thus importing a model as a map is most likely either really difficult or impossible.
But as I said I've used it a bit and there could well be an option for it. If you know that it's possible and are just having trouble with it, then I'm afraid I can't help you, sorry.
But as I said I've used it a bit and there could well be an option for it. If you know that it's possible and are just having trouble with it, then I'm afraid I can't help you, sorry.