Many of us know of the Louisiana Native Guard, a volunteer militia unit made up of New Orleans Freemen willing to fight for the Confederacy. They were not the only unit of freemen who wanted to fight for the Confederacy. At least 2 requests were made (in April of 1862 and November of 1863) to raise a unit of Mobile's creole landowners. All were turned down due to their racial ambiguity.
What if the southern leadership allowed for the recruitment of its Freemen population? Were they a large enough demographic to significantly alter the course of the war, as early as '62?
In my new book I'm writing
The Golden Circle 1: We Gained by Honest Toil, it's set in 1880, after the Confederacy managed to win their independence and are currently trying to establish "The Golden Circle" an overarching plan to bring Mexico, Central America and the Caribbeans into the Confederacy to create a Slave Owning Empire. The point of departure is that in late 1863, they accept Patrick Cleburne's proposal for raising black regiments and offering them freedom.
What happens is that they are able to raise up to 190,000 black men under the promise of post-victory emancipation. This frees up Southern Combat Regiments (aka white units) to join the armies of the Tennessee and Northern Virginia among others and are able to basically win several key victories in 1864, allowing for McClellan not only to be elected, but to defeat McClellan's own 1865 Spring Offensive (as McClellan wanted victory before he would discuss peace with the South). These defeats leads to the creation of the Treaty of Mexico City, with Emperor Maximilian II hosting the talks.
Now, the prologue itself, besides establishing these factors for victory, specifically deals with the Confederate Congress reneging on it's promise. They decide that only 1863 volunteers and 2 in every 14 of the 1864 volunteers are going to be given their freedoms. Everyone else and all the 1865 volunteers are going back into slavery. This leads to rebellions throughout the South of these angry slave soldiers, who were promised one thing, only to have it taken away.
The thing is, while maybe not so dramatically as I have it in my story, I don't think the Confederacy would have ever fully honored any commitments they made to negro soldiers. Negros were the lowest of citizens; I think Native Americans ranked a little higher in Southern regards.
But even in my story, they only helped out freedom of the South by freeing up the thousands of men that were in garrison duty across the South. That's only because the numbers were large enough to allow it. Unless they allowed a lot of African Americans into the ranks, it wouldn't have changed the outcome.