An aunt has asked the family not to serve alcohol because her son is fresh out of a rehab.
As a recovering alcoholic myself (sober over 16 years) let me try to address this.
First of all, it should be your aunt's son who makes decides himself whether he wants to go. I appreciate the fact that the aunt is concerned for her son, but he is the one who needs to work at his own recovery. Not that I'm saying that it's none of her business -- it's nice that she cares enough to ask -- but the final decision should be his. If he feels uncomfortable being around drinking, he should find something else to do (like perhaps opt to go to an A.A. meeting and be around other sober people, for example). If he feels confident in the fact that he won't drink, he should still ensure that he has a way to leave promptly (but politely) in case he finds himself overwhelmed by the urge to relapse. Make sure the car isn't blocked in by other vehicles in the driveway, for instance.
When I was newly recovering, I was invited to an anniversary party by some friends who I knew drank and used drugs. They were good friends, and I did not want to offend them, but was unsure what to do. I asked a friend who had been in recovery for many years, and he suggested that I go, but "make sure you have a way to bail out." I went, brought my own non-alcoholic beverages with me, and had a wonderful time.
If he is newly recovering, just out of rehab, remember that he has been in an artificial protective setting where no alcohol or drugs are present. He is back in the real world now. If he opts not to go, no one should condemn him for his decision. If he opts to go, I hope his recovery is important enough to him that he will remain vigilant and not be afraid to ask to leave if he feels uncomfortable.
The only other factor to keep in mind is, are any of the other attendees going to be drinking to the point of drunkenness, and if so, will they try to insist he drink? If so, best not to go just yet, until he has a little more sobriety under his belt.
Your aunt may also want to consider attending Al-Anon herself. They will give her excellent guidance as to how to deal with an alcoholic (recovering or not) in the family, and when intervention is necessary, or when not to meddle.
A lot of people do not understand the nature of alcoholism. It is a disease, not a moral deficiency. It is much more difficult to conquer than many outsiders might imagine. The alcoholic should not have to spend the rest of their life running from people with a bottle in their hand for fear they may "slip" themselves. On the other hand, they should not needlessly put themselves into situations unnecessarily where alcohol is flowing freely. The final decision should be his. Does he go to A.A.? If so, does he have a sponsor? It may be a good idea for him to call his A.A. sponsor and discuss the matter with them. Does he still attend after-care with a counselor from the rehab? Maybe he should call them to help him decide.