From what I have read, the main reason an officer or no would be issued a revolver is to prevent their men from deserting. The officer's weapon was his command (all the way from a Lieutenant's section to a brigade, division, corps, or higher), and if an officer had to draw his weapon to defend himself, he was either not effective at his job, or in a very desperate situation.
I also saw mention of the 1st and 2nd USSS. From what I have read, officers in those regiments were not only issued rifles, but used them. Every man, from the teamsters to the surgeons to the privates on up to General Berdan himself was an expert marksman, and that coupled with the rebellious attitude the regiments and the rapid, severe attrition of the units blurring the lines between the enlisted, ncos, and officers meant that they all viewed themselves on equal footing and all fought as riflemen.