On good behavior and early release, the honest answer is not likely. A violation of probation sentence is handed down specifically because the original conditions of supervision were not met. The judge already extended leniency once when probation was granted instead of prison time, and the VOP sentence is the response to that trust being broken. Most judges structure VOP time to be served without the same good time credits that apply to standard sentences, though it varies by state and by the specific terms the judge put in the order.
The rehab question is more interesting and worth pursuing actively, particularly in Georgia.
Georgia has a program called a Probation Detention Center, commonly referred to as a PDC. These facilities are specifically designed for probation violators who have underlying substance abuse or behavioral issues that contributed to the violation. They operate more like structured treatment programs than traditional incarceration, with programming, counseling, and rehabilitation built into the daily schedule. A 180-day VOP sentence is exactly the kind of case these centers were created for.
Whether your son qualifies depends on the nature of the violation, his history, and whether the sentencing judge is open to an alternative placement. The defense attorney needs to make this argument directly to the court if it has not been raised already. A formal motion requesting transfer to a PDC or an alternative treatment program gives the judge a pathway to approve it.
If there is any substance abuse component to the violation, that strengthens the case for rehab placement considerably. Get the attorney working on this now rather than waiting.