I am not a Georgia attorney, and you should consult one there to be sure of the consequences of these events, but I can answer this question as a general matter. Of course, this does not create an attorney-client relationship between us.
First, you should definitely inform your probation officer about the new arrest. They WILL find out, and it is better for you if you were at least honest about reporting it. Chances are that this was imposed upon you as a condition of your probation.
Second, there is a chance that your probation on the older case will be revoked, but it is possible that an attorney can help you avoid that consequence -- particularly if you have a defense to the DUI. If you are convicted of the DUI, however, it will be an uphill fight.
Make sure that your attorney on the DUI case knows that you are on probation. He or she must take that into account in assisting you in crafting the best approach to the case.
Its always better to tell them as soon as it happens than to let them find out by themselves. It also will likely constitute a violation of your probation, regardless of everything you've said. Sorry.
The outcome will depend on a number of factors: your probation officer, the judge, your underlying charge, and the strength of the DUI. If you have a good relationship with your PO, that can help, although most will tell you when they find out that they have to "do something". Telling your PO that it happened is usually the best case, but I would consult with an attorney licensed to practice in Georgia before doing anything: out-of-state attorneys who post on questions like these don't have the benefit of knowing the probation officer or judge. A DUI would be a violation of your general condition of probation "not to violate the laws of any governmental unit", but a local lawyer will be able to give you the true lay of the land.
Rule #1 on probation is always "do not violate the law." Probation does not have to wait to see what happens with your DUI charge to start revoking your probation. However, if you were wrongfully arrested, it is doubly important that you find an attorney to defend you on the DUI right away to prepare for an inevitable revocation hearing. If you tell your probation officer yourself, there is a greater likelihood that your officer will let you "walk in" to a hearing, rather than arrest you with no bond to wait for a hearing. However, warn your job and family that you're about to tell your probation officer, so that if you are arrested, they can find an attorney for you. Depending upon the county for probation and the new DUI, you may have to wait weeks in jail for a hearing.