Does anyone know if, perhaps, there is any list of staff at any of the hospitals?

I have a very elusive 2x great-grandfather named Henry James Simons. We believe his family was living in or near West Point, Mississippi during the civil war but we have been unable to find any record of Henry himself. However, he was a physician and family tradition says that he worked as a surgeon during the war and treated both Confederate and Union soldiers. We haven't been able to locate him on any Confederate enlistment roles. Could he have worked under contract to one of the hospitals?

Any ideas or suggestions on where to look would be most appreciated.