There were already quite a few black Southerners serving the army and navy in various capacities including as soldiers. One of the most notable was Louis Napoleon Nelson, a black Southerner who had fought in several major battles including Shiloh. Likewise there had been a regiment of free blacks from Louisiana who had volunteered and marched off to join the Confederates in the war. At one point I had a copy of a photograph of them in their gray uniforms. Perhaps I can find that again and post a link to it.
These things are often overlooked. It would do us well to learn more about them.
"When President Lincoln signed the Emancipation Proclamation in 1863, he hoped the document would discourage the use of slaves by the Confederacy."
He hoped no such thing! Lincoln could have cared less about blacks, and only instituted The Emancipation Proclamation to save his butt. I read all this in an older book. EP was ready to go much earlier but Lincoln saved it for a more politically advantageous time...