Disclaimer: I am not a mental health professional and my words should be taken as an outsider with experience, looking in.
When I was in grade school I had blackouts from rage. I would bet money that the reason the blackouts are occurring is either a lack of oxygen to the brain or an excess of oxygen to the brain. Either the blood pressure rises as the stress does and as the blood pumps harder, a sort of hyper-ventilation occurs in the brain which causes blurred vision and decreased brain function, which puts the body into a primal fight or flight mode, -OR- as stress rises the person begins to breath shallow or not at all, which causes the brain to suffer from lack of oxygen, and again puts the body into a fight of flight mode. (my issue was the over oxygenation)
Now how does that help someone deal with anger and blackouts? For me, understanding the physiology behind the psychology helps me to get a handle on what is happening around me. I would recommend anyone with this issue attempt to pay attention to their breathing when they start to become upset. Regardless of your issue, if you attempt to rebalance your oxygen intaken, you may be able to ward off the blackout.
For people who have to deal with people who have this issue, (not to be insensative or anything) be prepared to consider the possibility they are deflecting responsibility by saying they have blackouts. Our culture is ripe with inability to take responsibility for our actions. If medical and mental doctors are not able to diagnose or treat this issue, perhaps a trip to juvenile detention might help with their attitude.