Thanks for visiting the History-Sites.Com message boards. I promised my wife, really, that I would not participate in this discussion further. It makes me angry and frustrated to debate this point without my counterparts feeling it necessary to post any documentation of their position.
How in the world can I counter your "grandfather's" claim? You said it, it must be true. I must say, though I've read about Blacks affiliated with the Confederate army since the mid-1980's and have been a serious student of the Civil War since the mid 1960's, I did not realize how pervasive the Myth of the Confederate Black Soldier in other than negligible numbers had become. I also have never had so much trouble debating a subject that relies so much on accounts such as yours and the "eyewitness accounts", primarily of Northern press and politicians. It was a "fad" to make these reports, early in the war, you will note that these accounts of Black participation in Confederate ranks are confined to 1861-62, with the vast majority being Southern accounts of Freedmen offering their services to the government and pledging allegiance to the South and it's Cause.
Unfortunately, for the Southern war effort, the Confederate government and army officially, clearly and legally, denied the use of Black Confederate Soldiers until February of 1865, when a few companies were recruited in the Richmond area, were barracked at a Richmond prison and never saw combat.
I'm sure your ancestor was a wonderful man and I honor his memory. Unfortunately, since the mountains of evidence, or lack thereof denies the existence other than a handful of Blacks in Confederate ranks, I take this story "with a grain of salt."
Now I will go apologize to my wife.