Neither Robert E. Lee nor Jefferson Davis ordered the execution of black union troops..

Sorry, Bobert, but that's a bit disingenuous. You're forgetting Fort Wagner, Fort Pillow, and a host of other cases where Black Union prisoners WERE summarily executed by Confederate troops. It was only after Lincoln made it clear that he would execute Confederate prisoners in retaliation that the practice became less than universal.

The Confederacy DID make it official policy that any Black under Union Arms was ipso facto a slave, and thus had no rights whatsoever, & thus no crime to execute a "thing". Which threy often did.

Check out that two-legged piece of excrement Nathan Bedford Forrest, for example.