I found an interesting discussion on the Tennessee Board. It concerns Union soldiers, mostly from Minnesota. It seems that as prisoners in Andersonville they were enlisted into the Confederate Army (10 TN Infantry CSA). To escape conditions there it seemed they were willing to fight Indians and do guard duty. I knew about Galvanized Yankees (Rebs who fought against the Sioux and that to get out of prison but had never heard about this). It seems that it was implemented by John Bell Hood. George Martin is the one who presented most of the information.