I have to correct my post just a bit. North Carolinians did not join the 51st Indiana although 10k did join the Union Army or Union homeguard units. Per Dean Barber 1stalabamausv.org approx 5k white Alabamans joined union regiments from various states and then the Union established the 1st Alabama USV Cav. So yes any white man from any state could at least attempt to join a civil war regiment of a different state or region and have a good chance of being accepted. Also see "A Southern Boy in Blue the memiors of marcus woodcock 9th KY USV he and many of the men of the 9th were from Tenn.

Leonard