You know, I hadn't thought about that. He was Voldemort's roommate, wasn't he? A good friend, if nothing else. That would mean that Hagrid was Slytherin. I never saw Hagrid as the ambitious type, just as a lovable big lug with a badass motorcycle and trick umbrella. (Hmmmm, Hagrid would've fit in on the 1966 version of "Batman" on TV.)
Don't think he was Tom Riddle's roommate. Hagrid was expelled in his third year. In Book 2, Riddle was a sixth year when Hagrid got the boot.
I can't link to the exact page, but if you click the site link, then click on A-Z Index, then H for Hagrid, then Hagrid at Hogwarts, you'll see where I got the info. :)