There is next to no evidence that slaves actually fought for the Confederacy.  It wasn't until like early 1865 that the Confederate Congress approved conscripting slaves as war fighters.  Apparently,  only two companies of black troops were drilling in Richmond when Lee surrendered at Appomattox. 

Hell, even in the North, there was considerable resistance to arming black troops to fight for the Union, although eventually something like 190,000 black men fought in the Union Army and Navy. 

You need to check the record about Lee being anti-slavery.  Rich slave owners like Lee, and Jefferson and Washington,  found themselves in a situation where their personal feelings about slavery were of little consequence.  More and more often before the war, state and local laws actually forbade freeing one's slaves in one's will, or even freeing them at all, particularly en masse. .