no but they can break combat and mezz or use their stun opener (only once per fight cuz of cd though; scrapper's cd is considerably shorter). ops don't even need to break combat. they can flash grenade.
That only applies in a 1v1. In a group battle they can't vanish and mez you because them vanishing won't remove you from combat since you're fighting other people.
It's also just a 1.5s knockdown which honestly is not a big deal since that's as long as the GCD, but far too many idiots go "OO EMMM GEEE" I'm stunned, must break it with cc break. I luls at these bads, especially in huttball when I pull them onto pit, use spike, laugh as they cc break it, and then use my real stun and watch them die.