There is no specific group for hackers as the hack can be used in all instances; PvP, and PvAi; but the most common set-up for a hacker in co-op is OPK or position kill. What OPK does is it 'attacks' the heads of all enemies on the map as they spawn, and most of the time kills them instantly. But it has a set damage and in missions like Death Vally, the last boss can take upto 20 seconds of direct OPK before it dies.
To answer your EXP question, no. If you are hacking you will get kills, and conciquentially, exp.