I think the reason some people don't know about hitmontop is it is so OU no one uses it anymore but since its use went down, people figured it was safe to play it again. just my explanation, anyways.
I've seen a lot of Volc + Hitmontop combos. And people use Rock Slide to much, its not as good as it seems unless its STAB, then it is OK. doesn't it have like 75 BP? Unless you want to flinchax that much, I'd use Stone Edge.