well there are definitely some viable pokemon that resist rock in doubles, its definitely not an unbeatable strategy. Swampert, hitmontop, rhydon, metagross all see some usage in doubles and can really shut down a rock slide flinch team when they get a free switch in on a cb rock slide from aerodactyl. Rock slide damage is also reduced in doubles (ty gen 6) making it a lot weaker, but still very annoying to have one of your pokemon flinched.