Chaos dwarfs have tons of greenskin ,,slaves". But because they ARE after all greenskins, they are realy, realy awfull as slaves. Hell, the reason why the CD created black orks is so they have better, smarter and (most importand) more disciplined slaves and that nearly cost them there capital city!

Alsow, Hobgilins worke for the CD. They even backstabt the black ork rebellion, saving the asses of the CD's.