His attempt during the Dark Reign actually illustrates why he would be an effective leader. He took a bunch of unruly misfits and forged them into a highly efficient military unit capable of challenging hordes of undead and mythical creatures. And the reason they died is not because of Ares per se, but rather due to the loyalty he inspired in them which made them come back for him after they had already escaped.
I could see Ares as a combat leader as well as the enforcer and mentor type but they would need someone to act as the face of that team because Ares would not do well in that role.
@sc: I do believe leadership would be a burden on him, as you say. During the Dark Reign arc, his role as leader/Mentor of the Shades, he is not nearly as reckless as he is generally displayed to be and has a genuine concern for them, a concern which ultimate gets him captured when he most likely would not have been had he been alone or not responsible.
Umm, they pointed out before hand that they were going into a unknown situation without proper backup or intelligence. Ares rode into the mission on a giant bomb letting everyone knows they were there. They were unprepared to face Ares's maniac son or hordes of undead. Ares himself admitted it was his fault at the end that they were all dead at the end. The other attacks he led when an Avenger had similar results. He fails to take full advantage of his resources coasting his side much higher casualties then necessary. Something he was called out on several times. At best, Ares can act as a drill sergeant to whip troublesome recruits in line, but actually lead a mission and expect to get your soldiers to live through it, mission planning, or anything to do with actual leading would have to go to someone else.
Yes, in a rare showing he did display concern for them. One impression I got though was he knew it was his fault that they were in over their heads because of his blunders. The problem with trying to assign him to any team is Ares has displayed blatant disregard for orders or mission objectives when it clashes with what he wants that he is too much of a loose cannon to place on any team.