You, sir, have made a great find! His records state that Wiley Stewart, a Free Man of Colour (a Black Gentleman) was a soldier in Capt. Q.C. Sanders' Company of Tennessee Cavalry, CSA. He mustered in 22 July, 1861 and was enrolled 24 August, 1861 at Camp Zollicoffer by JW McHenry for a period of 12 months. His company later became Co. H, (Murray's) 4th Tenn. Cavalry.
I have also tried to find your ancestor in the 1860 Census, but have had no luck. However, I did find that most of the people spelling their name as Guyon on the census were in NY. I will try to dig up some more info.