HUSKERBLITZ; OK, the G.W.Reeder is George W. Reeder.
You questioned if the soldier on the right might be Johnson Garvin; Nope. The record in the NPS site lists him enlisting in KY 22nd Infantry , Company D as a sergeant, later promoted to 1st Sgt. The record for him in CWData.com says he enlisted as a corporal, later promoted to 3rd SGT. While these records do differ, neither lists him as a commissioned officer. Thus, both Yanks in the pic are wearing officer's coats, but neither yank we have researched achieved officer's status, so the "identification" given for the photo is wrong for both soldiers.
Of slight further interest: The NPS sites lists both a Garvin, Johnson and a Gavern, Johnson listing them as alternate spelling for the same man; the records are almost identical. CWData got their info from the Report of the Adjutant General of the State of Kentucky, and I suspect that the NPS used the same source.