If he did not go before a judge and defend himself against the charges then I don't think the domestic abuse charge can stick as far as purchasing a firearm is concerned. However, I am aware of one person that got denied a permit for being arrested for Domestic violence and was denied a license on "good moral character" grounds. If it were me I would go into a gun store and purchase a firearm. If it goes through, good. If it does not then ask the dealer who should I talk with to get it straightened out. As long as you answer the questions on the form truthfully, you are not breaking the law.
If/when your buddy decides to pursue firearm ownership, tell your friend to run a background check on himself by a credentialing agency, such as Choicepoint. Something similar to National Criminal File background check. Obviously he's statutorily disqualified if certain types of convictions, and perhaps arrests, appear there. I'm not that firm on GA firearm law and IANAL so I won't bother to comment further on the topic of disqualifiers. But because all counties/states didn't report electronically during the time of his incident (some still don't) he should additionally request the hardcopy records for the county in which he suspects there may be a disqualifier (assuming nothing appeared in the National check). Recommend that he request from the applicable county clerk his complete criminal history. If there are no disqualifiers there then he's all set. This is the process I used when I wasn't sure about how an incident from long ago was recorded (turns out it wasn't even an arrest in my case). All in all the process took about six weeks and fifty dollars. That instead of paying your favorite attorney for one hour of service.
You can also run a background check on yourself at the local police department. O.C.G.A. §35-3-34 (d.2) provides public access to felony conviction records without consent of the person whose record is being checked. Local law enforcement agencies may provide this information for a fee not to exceed $20.00. The subject's full name, race, sex, and date of birth must be provided at the time of the request. A complete Georgia record may be obtained with the individual's consent. A signed consent form from the individual whose record is being sought must be provided to the local agency. Fees vary. More info: GBI Official Page regarding Criminal Histories http://www.state.ga.us/gbi/crimhist.html (Please contact GCIC's Criminal History and identification Services at 404-244-2639, Option 2, for further information) If you want out of state records, you need a national database. This is going to require two fingerprint cards and an $18 fee. For more information, the FBI's web site on this issue is http://www.fbi.gov/hq/cjisd/fprequest.htm . You also can contact the FBI at 304-625-3878. I hope this has been helpful.