Roster of Confederate Soldiers, 1861-1865 shows:

Oates, Samuel W. NC 55th Inf. Co.C Sgt.

This does not mean that Samuel K. Oates did not serve, only that he is not listed in the NARA records.

Conpendium of the Confederate Armies - Tennessee - pg 61 by Stewart Sifakis

TENNESSEE 12TH CAVALRY REGIMENT
Also know as: 1st Partisan Rangers Regiment
12th Partisan Rangers Regiment
ORGANIZED: behind Union lines in West Tennessee, in part from Burrow's Cavalry Battalion, State Troops, on February 14, 1863. Reorganized Feb 4, 1864. Consolidated with the 3rd Cavalry Regiment. Reorganized, and Company "C", 2nd Missippi Partisan Rangers Regiment, and designated as the 3rd Cavalry Regiment Consolidated on Feb 13, 1865.
FIRST COMMANDER: Robert V. Richardson [Col]
FIELD OFFICERS: George W. Bennett [Maj]
Berry B. Benson [Maj]
Reuban Burrow [Maj, LtCol]
John U. Green [LtCol, Col]
Primarily assigned to Richardson's Brigade, Forrest's Cavalry Corps, Department of Alabama, Mississippi and East Louisiana
Further Reading: McLeary, A.C. - Humerous Incidents of the Civil War