When I stated "It was not until General Grant took overall command in March of 1864 that former Confederates who enlisted in Northern units went out West." this was not entirely correct. The 1st Connecticut Cavalry had two companies mostly made up or former Confederates at Fort Delaware in 1863 and did fight on southern soil mostly in Virginia. What I should have said was after General Grant took overall command of the Union Army those former Confederates that enlisted in the Federal Army were sent out West.
Yet there were some like the 11th Ohio Volunteer Cavalry in 1863 that had recruited former Confederates from Camp Chase and sent out West. In my opinion the 11th Ohio Cavalry was smart on how they enlisted the former Confederates. They salted the company with former Union guards at Camp Chase. If a former Confederate had deserted there was not a need for a physical description notice as the soldiers knew exactly what they looked like.
There were many galvanized Union units in various organizations and came from almost every major northern POW Camp. Fort Delaware had at least three or four units alone but the 3rd Maryland Cavalry remained the largest group of former Confederates who would fight on southern soil.
Many of the junior officers in the 3rd Maryland Cavalry resigned rather then to lead former Confederates, some back to their native States. The Union Army gave repeating rifles to the former Confederates and a junior officer having his back turned in leading a charge may have wondered about his chances of surviving. Captain Andrew J. Pemberton was one of those officers who resigned. At least one former Confederate was given a commission as an officer in the 3rd Maryland Cavalry and it might have been awkward saluting a former enemy and having been a loyal Union soldier from the beginning.
Needless to say there were many desertions within the 3rd Maryland Cavalry. One soldier who had been a Union soldier from New York had deserted at Gettysburg and claimed to be a Confederate. He would later desert the 3rd Maryland Cavalry and enlisted in another unit and then deserted that unit. President Lincoln authorized a proclamation in 1865 saying that all Union deserters would be forgiven if they returned to duty by May of 1865. This soldier turned himself in to the 3rd Maryland Cavalry and after the war went to Canada. While in Canada he applied for and received a Union pension. LOL prior to deserting at Gettysburg this soldier had a number of prior desertions.