Ralph,
Andersonville didnt start up until March 1864. I looked at Andersonville and his record from History of PA Volunteers 1861-1865.He is shown as deserting on 7/2/1863(probably captured and not present). The 11th PA Cav was a 3 Year unit. Hiram enlisted 8/20/1861 so he would have had another year to serve. Nothing connects but stranger things have happened.
Maybe his confinement was at another prison and by 1912 they associated it with Andersonville.
Mark Davis