Remember the Union forces were segregated, even on the battlefield. To give "Volunteer" status to black regiments would imply they were of equal worth and would be available to mix companies and regiments with white volunteer brigades in a battle. I do not believe this the case. I believe they were considered a separate corps of the Union armed forces. Tennesseans, even Unionist would not have fought together with black companies or regiments. Correct me if I'm wrong.