It depends on a few things. First, do you have extra frozen rats lying around?
If so, it would probably be best to thaw one out first. It's a bit difficult to tear one up to eat if it's as hard as a rock.
Second, it depends on what kind of hawk you're trying to lure close. I could see a red-tailed hawk coming down for a rat, but maybe not a Cooper's hawk (they mostly go for birds). If it really starts to smell you might get a turkey vulture.
Of course if you leave it out overnight you could get all kinds of other critters. But if hawks only went after live food it would be a lot harder to have them in zoos.
Oh, and if you put something out, try to avoid stuff like chicken or beef. Or any meat without skin and fur, really. Nasty stuff like hair helps to clean their "stomachs." And a hawk might not recognize a processed carcass as food, like we do.