There were slaves who were used as support (getting materials, cooking, etc.) for the Confederates. But in 1864 Robert E. Lee tried to raise a Black Confederate Army. While there are reports of Blacks fighting for the south, the Black Confederate Army was not raised-especially like the Union raised all-Black units. Lee's idea was that the men would be guarenteed their freedom. But understand that this would have gone against the Confederacy's idea of White supremacy of letting the men fight.
Indeed the history of the Civil War is more complex than many people think. Note that the Union did not raise all-Black units until 1862. The Confederate victories of the two Manassas, or Bull Run, Battle convinced Lincoln and others that Black men must be allowed to fight in the war. While Lee was personally against slavery (or so it says), William T. Sherman, the Union general who went through Georgia, was for it. Blacks could face as much bigotry from northern soldiers as they would the southerners.
Note that Lincoln went into the war to preserve the Union. If he could perserve the Union by keeping slavery, he would do it. No matter how one tries to twist it, the war's central issue was slavery.
BTW I just started reading The Negro's Civil War by Jaqmes M. McPherson. The first edition was published in 1965 while the second was published in 1990. There is another book called (I think) Men of War written by Trudeau. This book is very long.