Hook up with the guy you like, or with a different guy?
For me, if I like a guy and he doesn't feel the same, hooking up with him rarely works (once in a while it does, but I can usually tell if it will or not - it's a gut feeling).
If I like a guy and he doesn't feel the same, I may hook up with someone else. That actually tends to help me. I'm not sure why. Maybe I tend to get more crushes on people when I'm in a bit of a dry spell?
I'd go with what your instinct is. If you really feel like it'll help, I'd go for it.
If you think you'll end up feeling hurt if he doesn't want to date even after you have sex, I'd avoid it.
Good luck!