There was one. His name was Aleck Kean. He came to the Howitzers with his master John H. Vest. Vest was killed in 1863. Kean remained with the Howitzers, evidently as a cook.
In a 1912 article in the magazine Confederate Veteran, Judge George L Christian states about Kean “I affirm that he was the most faithful and efficient man in the performance of every duty pertaining to his sphere that I have ever known. His whole mind and soul seemed bent on trying to get and prepare something for his mess to eat; and if there was anything to be gotten honestly, Aleck always got the share which was coming to his mess, and he always had that share prepared in the shortest time possible and the most delicious way in which it could have been prepared in camp. The comfort of having such a man as Aleck around us in those trying times can scarcely be described and certainly cannot be exaggerated.”
I would say that it was doubtful if Aleck Kean ever served on gun crew with the Richmond Howitzers.
And has been pointed out, the Confederacy used blacks in a number of supporting roles, including as cooks and servants. That didn't make them soldiers, and the Confederate army didn't consider them to be soldiers.