Given this man's age, occupation and family situation, it's unlikely he would volunteer for military service. As an overseer this man could remain out of the army for the duration of the war. I don't see his name in the Confederate Citizen's File, either.
Based on the 1860 and 1870 census of men named Gill who were of military age, it appears that all five enlisted in Co. "B", 11th Georgia Regiment, William C. Gill being elected 1st Lieutenant of that company. My attention is drawn to Green Gill, a veteran of Co. "B", 11th Georgia Regiment, who appears on the 1870 census of Lee County as age 47. His name and household doesn't seem to appear on the 1860 census, just as Henry G. Gill's name and household isn't found on the 1870 census. In 1860 Henry G. Gill reported his age as 38. I wonder if his middle initial "G" stood for Green.
Do you know the answer?