See section 3 of the act of 17 July 1862, which required officers to deduct from their own pay each month the amount the government paid any soldier employed as an officer's servant.
On 28 September 1863, "J Jamison", of company H, was detailed as Colonel Gregory's servant; this may be John Jamison [who was transferred to the VRC on 1 July 1863!], or David Jamison; both served in company H.
On 29 September 1863, Gregory reported that two enlisted men were employed as cooks, and one as a hostler: Joseph Johnston as Horace Faust's cook, Philip Toushant as John Donnell's cook, and John Jamison as Edgar Gregory's hostler. (It may be relevant that Gregory had just returned from a leave due to wounds he received at Chancellorsville, and Donnell was wounded at Gettysburg, and had not returned to the regiment at the end of August.)
On 14 November 1863, Gregory reported that five soldiers were acting as servants, cooks, etc., and one had been: James Jameson, co H, was Col Gregory's hostler from 29 September 1863 to 16 October 1863 [Bates lists no James Jameson; see John Jamison and David Jamison]; Henry Schaefer, co A, was Col Gregory's hostler beginning 17 Oct 1863; Edward Gamble, co B, was Morris Kayser's cook, beginning 28 Oct 1863; Joseph M Johnston, co D, was Horace Faust's cook, beginning 1 Oct 1863; Joseph Rementer, co E, was Matthew Hall's cook, beginning 6 Nov 1863; and Philip Tousant, co I, was John Donnell's cook, beginning 25 Sep 1863
On 30 December 1863, Sellers reported that 6 soldiers were acting as servants, etc.: Henry Schaefer, co A, as hostler for Edgar Gregory, since 17 October 1863; John Coster, co A, as cook for Francis Gregory, since 10 December 1863; Edward Gamble, co B, as cook for Morris Kayser, since 28 October 1863; Joseph M Johnston, co D, as cook for Joseph Sinex, since 16 December 63; Joseph Rementer, co E, as cook for Capt Hall, since 6 November 1863; Henry Dunn, co I, as cook for John Donnell, since 18 December 1863 [letter].
On 24 March 1864, the only enlisted man serving as an officer's servant was Robert Ross (co I), who had been his hostler since 6 Mar 64 [letter, Sinex to Fowler, 25 Mar 64]. [He was detailed as Sinex's hostler only on 26 Mar 64]
On 25 April 1864, two enlisted men were serving as hostlers, servants, etc.: Robert Ross (I), Sinex's hostler (since 6 Mar 64), and William Harris (I), Lt Donnell's servant (since 16 Apr 64) (report, HQ 91st PA, 25 Apr 64).
On 8 July 1864, John Boyer (K) was reported as captain's cook, and John Coster (A) was reported as an assistant cook (perhaps still cooking for the company captain?) On 9 July 1864, John Coster (A) was reported as servant to Captain Gregory