I versed a stealth team last night in GW with Teebo as leader. It got to a point where the whole team was stealthed and when I had my turn to attack it auto targeted the character furthest to the right of the screen. Which was Chewie. I also found that characters only stay stealthed for 2 turns and when they come out then that character becomes the only character you can target.
But then I suppose if you have 2 healers you might be able to have the rest of the team stealthed and attacking whilst you heal/atk/etc.
I found it annoying at best as AI was doing the attacking and so forth but if its user controlled it definitely has potential