You son can't be the only one that has been in this situation at the program. I would definitely ask what they suggest as far as aftercare and a possible step-down living situation.
Having said that, I think limited help on a short term basis would be okay. With my daughter, my therapist suggested something like the first month rent, then half the next month, then a quarter the next month, and then on her own. He can also apply for food stamps. You don't want to set him up for failure and since he has done his part (9 months sober and finished the treatment program), I don't see any problem with a little help to get on his feet.
Worried sick, I don't think people were saying you shouldn't help when the loved one is doing the right thing. In your son's situation, he has returned to the same setting with a drug using girlfriend so I think the posters were worried that helping him with the rent would be enabling the same behaviors.
lovemyson1, I am rooting for your son!!
~Kathy