I sent you my two lists that I compiled - did they get there? One is non-military prisoners who died at Andersonville, so you can pretty much rule them out as having been at Millen; the other is non-military prisoners who survived Andersonville and I'm sure that at least some of them ended up at Millen. If memory serves, the two lists together add up to about 300 guys, or just .006% of the 45,000 prisoners held there.
Most were teamsters, but there were a few railroad workers and at least one telegraph operator. Farmers would sometimes sign on with the Quartermaster General to serve as teamsters during their winter months. Alas, if they died - at Andersonville or elsewhere - there was no provision and no pension for their families, leaving their widows and children in dire straights, indeed.