Posters are getting hung up on labels (again). Whether he's an alcoholic or not is irrelevant. I'm inclined to agree with Eco on this, he may just not think that DUI is a big deal.
Of course, that just makes him an asshole. This isn't about personal risk, its about making decisions for himself that put others at risk. For that, I hope your BF goes to jail for a very long time. Its one thing to decide to ride a bicycle without a helmet and smash your own brains in. Its another thing entirely to operate a 2000 lb vehicle and potentially kill someone else's wife/husband/ or CHILD.
So, I would definitely confront him about this and let him know you think its a dealbreaker. If he can't be responsible about this, do you think he'll be responsible in other areas of your life together?
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh