Keeping your child safe physically, mentally and emotionally has to be your first priority and if there is a history of drinking and driving then there is great cause for concern and action. Usually an arrest for DUI results in immediate loss of driving priveleges and if he adheres to the law you don't have to fear he will drive with your child in the immediate future. A blow machine is likely in his future and that will give you some peace of mind.
Your son working through the complicated emotions of an alcoholic father while coping with the normal stress of growing up is hard... I put my kids in counseling and they benefitted greatly from it. I also studied the subject and tried to be as helpful as possible with not making it harder on them by encouraging them to be understanding and forgiving of the illness while setting their own boundaries.
Hoping for the best ... maybe this will be a key to the future and some postive changes will result.