They could of course but isn't that the same with any group? Or is a 4/5 shaman group completely invincible?

IMO any single player can be beaten by a group of players (assuming they know how to work together), irrespective of how many characters that single player is actually controlling. Or multi-boxers would be god like in PvP.

So yeah two or three hunters that are being played by someone who knows how to play should, by my calculations, be quite fun in PvP, especially now that Dead-zone is all but gone.