Walking to Shiloh from Corinth sounds like fun. I live 110 miles from Shiloh and have been there many, many times. Over the years, I have learned to never go there on April 6 or in July or August. Actually the best time is in November or December (no leaves or ticks) and use a trail bike to get around the battlefield. I like to take a unit on either side and follow their route for both days of the battle.
With regard to Ft. Donelson POWs, I have documented 757 that took the oath (many rejoined their units later as the choice was taking the oath or dying in prison). Additionally, I have documented 180 POWs thus far that took the oath and joined the Union Army. Many were Irish from the 10th Tennessee and several of those were sent out west.