"If that makes me a horribly enabling parent - oh well. I'm pretty comfortable with the fact that my parenting did not make him an alcoholic."
You're right, you didn't Cause it. But you also can't Control it, and can't Cure it.
I don't think you truly mean "oh well". You want him healthy and safe. But as long as you do all the work, and continue to enable the disease, then it's difficult for him to "get it" and figure it out for himself. I mentioned in an earlier post that my parents did exactly that for my brother. It started in his early 20's. My Mom said everything you're saying. So today he is 49 and still an alcoholic, living with them, and my parents are still saying all the same things.
He won't be released without a discussion about his options. But it's up to him to take what they give him and follow through. I agree that it's off base for his sponsor to meet with you, he is crossing boundaries. Your son should contact him when he's released, and they should meet.
I'm sorry you're going through all this. The only way through something is through it.