Of course, the Confederacy ignored 1 million man pool that could have been used to replace their losses. The Southerners preferred to keep them slaves. The North used these same men to fill their ranks and man their ships.
This is mostly true. There were efforts to start using slaves as combatants but by the time they started getting serious about the idea, it was already too late.
Of course Nathan Bedford Forest actually did use about 26 of his own slaves as cavalrymen and promised them all their freedom at the end of the war, no matter which side won. 25 of them remained with him throughout the war with only one deserter.
I found a wonderful essay on the topic a year or so ago, and I wish I had saved it or a link to it. It also said that Nathan Bedford Forest actually wrote out all the manumission papers before the eve of one of his battles, so that if he was killed in the action, his promise would still be kept.
But yes, the Confederates hamstrung themselves by some of their own social ideas, and failing to use their slaves to staunch the loss of manpower was one of them. The idea not only didn't fit into their social structure, there was probably a great deal of fear of the idea in terms of armed slaves initiating a revolt.
Just the fact of slave soldiers would have inspired others who remained on the plantations, and it might have destroyed their system anyways.