Yes, he is enabling him. He loves him, but he's enabling him. Fact is the guy is never going to get better, will keep hurting himself and others as long as people make it easy for him.
Just look at the facts of this man's behavior.
TWO DUI's, court-ordered AA. And it sounds like most of his regret in regards to this is just about losing his license. He could have killed someone or himself, and the first DUI sure didn't make a dent. Any indication that he doesn't want to drink anymore for himself and the safety of others, or is it just all about getting the license back? Add to that, he had no money to support himself, but clearly found a way to get money to drink. In short, so far he does as much as he can get away with until someone forces him to do something about it i.e. court punishment. Helping him get his car/license just puts him on the road again, without any real assurance he won't do it drunk again (and giving him money just makes it easier for him to buy alcohol). People deserve a second chance, but again...given his history you've posted, that he's blown second, third, etc chances you've given him, what indication has he given that he will do anything but what he wants regardless of how it hurts others? How would your DH feel if he helped his brother get his car back and he ended up hurting someone with it while driving drunk?
He won't take care of himself knowing he has diabetes. I would say "his choice", except that that choice is costing other people not just stress and pain, but costing them money. He obviously doesn't care that he's doing that to his siblings (and his mother before that). He just figures someone will bail him out.
He has children he clearly puts himself before (not taking the opportunities to straighten out his finances, putting his life at risk, etc). If he can't even put their needs before his own selfish ones, why in the world would your DH think he's suddenly going to be a different person. If your DH really wants to help someone in need, he should offer some support to his niece/nephew, the REAL victims in all this.
In short...the guy just has no urge nor any drive to "be different." Why should he? He gets a free pass, others take care of him and his obligations, and that's a pretty sweet life. And honestly, even if he's just suffering from a massive lack of self-confidence, doing things for him isn't going to help him feel better about himself.
I don't doubt your DH loves his brother, but if he really wants to help him, he'll stop making it easier for him to fail.
I feel for all the guilt and confusion your DH must be feeling. You have my sympathy for your situation.