Hunters do have their use on several maps and are brought along since MoP hit. Rogues and ferals bring stealth altough rogue's argually are a better choice because of smokebomb.
No, it's melees in general. No good reasont to bring them to an RBG most of the time except as flagcarrier/for smokebomb and such. While being fairly strong in Arena and 1on1 situations they get worse as more casters are present because they have to actually reach their target before they can start inflicting damage.