Which historian has argued that significant numbers of black troops fought for the CSA? Where? Using what sources? You're making  a fabulously provocative claim w/out any sources. 

The only thing I know like that concerns a group of free men of color in New Orleans who tried, unsuccessfully, to enlist in the Confederate forces as a unit, The Louisiana Native Guards.

When Union forces took New Orleans in 1862(?) however,  the Native Guards enlisted in the UNION army. They guarded POW's in coastal Mississippi and fought at the Battle of Pascagoula . . . for the Union. 

Black Union troops fought heroically at any number of battles, often suffering horrendous casualty rates: Port Hudson, Fort Pillow, Battery Wagner, Nashville, the Battle of the Crater and others. 

Where did black CSA troops do this?

http://www.historynet.com/african-americans-in-the-civil-war