What is interesting are the sentences immediately preceding and following the section quoted earlier:

"The most liberal calculations could not give them more than 64,000 men. Over 3,000 negroes must be included in this number...[insert earlier quote]...They were seen riding on horses and mules, driving wagons, riding on cassions, in ambulances, with the staff of Generals, and promiscuously mixed up with all the rebel horde. The fact was patent, and rather, interesting when considered in connection with the horror rebels express at the suggestion of black soldiers being employed for the National defense."

First, Steiner overestimated the numbers in Lee's army at 64,000, not including another 8,000 under Hill that he notes as coming through a couple of days later. According to Stephen Sears, the ANV entered Maryland with at best 50,000 troops; by Antietam it fielded in the neighborhood of 35,000-38,000. This was at a time when the Pinkerton and McClellan were estimating the ANV at 120,000-200,000. See Stephen Sears, "Landscape Turned Red: The Battle of Antietam," p. 69 & 389 (Ticknor & Fields, NY 1983). Estimates such as those Steiner, a civilian, made are notoriously inaccurate - consider the estimate of a Confederate soldier of 2,000 USCT killed at Fort Blakely when in reality only a tiny fraction of that number were slain or modern guesstimates regarding the numbers at rallies, protests, etc... This being the case, it is likely that he overestimated at least as bad if not worse the number of blacks that he says were "promiscuously mixed up" with the ANV.

Second, the description of the blacks, i.e., riding mules, driving wagons, on General's staff, suggests that they were being used a servants and laborers rather than as soldiers. Whatever their actual number, considering the lack of evidence from Confederate sources couple with Confederate policy, it is more likely that the arms Steiner noted were being carried for their masters rather than as their personal arms for fighting.