To be fair, most of these are references to putting slaves &c to work building fortifications, driving wagons and providing auxillary support. Southern newspapers often include notices to planters that slaves were wanted for hire on military construction projects. Obviously officers in Federal service could see the value of doing the same.
In addition, officers and men brought slaves with them into the army. Of course anyone who did so had to provide food and other necessities. When rations became short and the government cut short rations in half, most slaves who came to the armies were sent home.
Confederate authorities drew the line on actual enlistment, not just of black men but anyone "of mixed blood." All Americans of that day were extremely sensitive to issues involving race. In Mobile for example Art Bergeron mentions Creole petitions to provide militia service, which were not accepted due to their race. Confederate service files show that men reported to be "of mixed blood" were discharged strictly on that basis. For exampl, a man named Innerarity in the 15th Confederate Cavalry was sent home for that reason. The same is true of Alabama commands in the Army of Northern Virginia and the Army of Tennessee.
It took an act of Congress to get blacks into the army as musicians. In March 1865 it took another act of Congress to authorize recruiting slaves for actual military commands.
Back when I had access to one of the best libraries for Southern history anywhere, I took several sources cited by "Confederate Negro" advocates and examined them. One of these was the U.S. (of course) source that had the Richmond Howitzers being manned by black men. Other than battery cooks, histories of that command do not support this assertion. There's lots more, but I would have to look for other references.
One day I would like to examine records of Capt. Addison Harvey's company (Forrest's Scounts) to determine the truth of claims that his command included a number of black men. Harvey was killed by citizens in Columbus GA shortly before after U.S. forces left the city in April 1865. If you're asking my personal feelings, I'd like to determine that this "Confederate Negro" story was true. However, like any other claim, I'll have to go with the evidence regardless of what I want to believe.
From time to time a slave or free negro might have picked up an Enfield as mentioned at Harpers Ferry. Except in auxillary service and hired men working on fortifications, such as the "Forrest negroes" sent to Mobile in late 1864, I have a problem with anything more than that.