You are in Member Communities . Unless your son is also suffering from depression, ADD isn't going to be an obstacle in dealing with grief.
Anger management is a different topic though.
ADDers often do have a problem with controlling their tempers. From what you are saying now, it would appear that your son does have some coping skills and was using them until a year ago. The thing to remember about coping with ADD is that it is an endless uphill battle. It would appear that he lost the will to continue the fight. A lot of ADDers never get close.