I think his sword should be able to cut him. Even if not Volstagg is an experienced enough warrior and has fought enough monsters to deal with the Rhino. As questionable intelligence Volstagg may be Rhino is even dumber.
Rhino has the biggest range of showings in such a short span. He'll can get punched out by an angry Spider-man or knocked out by a speeding car in one instance and come back six months later and look completely invulnerable.
Crediting him with a class 75 average, I think Volstagg could beat him. Asgardian weapons would cut most class 75 characters, but Rhino seems to have very good piercing durability. I don't recall him ever being cut by anything. Given his huge number of appearances and that writers use him exclusively to job, I have to credit him with being invulnerable to bladed weapons. However, I see no reason why a warrior like Volstagg couldn't attack his face, which is exposed. Rhino apparently has superhuman durability even without the hide, hence the reason he doesn't die when punched in the face, but my impression was that he's far less durable than the hide he wears.