Well, I'm not quite sure what you're trying to prove, here. There were no Native Americans living in what is now Greenbrier Co in the late 1700s. The raids were carried out by the Shawnee and they made most of the journey by canoe from Ohio. They did not attack with bows and arrows, either, so whatever you've found it is extremely unlikely to be related to those raids and is very likely to predate that era by centuries, if not millennia.
With all due respect, those grants in Sims's book are not for military service. Look at his p 144, second from the bottom: 400 acres on Sinking Creek to James McCoy, in 1790. This tract was in consideration of a "certificate in right of settlement", not a bounty for military service. These ceritificates were awarded to those who could prove that they had settled in what is now Greenbrier before it was legal to do so. I don't know for a fact that money changed hands, though I strongly suspect that it did. All the Virginia military bounty lands were in Kentucky, I think. There were bounty tracks set aside in Ohio, but I don't think those were for Virginia service.
I read through a half-dozen or so of Captain Lewis's earliest grants in Greenbrier and he paid cash for all the land I saw. Do you have a specific tract in mind that he might have been awarded for military service?