I was in your shoes many times. I would help him out if I were you. I’ve forwarded many resumes to HR while working at Big Four and it was really no big deal. Typically I would inform the HR that I personally do not know this guy and that I met him only once or twice but that this guy asked me if I could forward his resume to HR. The HR will respond accordingly. The firm won’t hire a guy simply because I forwarded his resume to HR. The HR will assess him along with many other candidates, so he will have to be marketable on his own.