I was the one to suggest the orc inclusion as plantation workers.  However I rather suggested that the orcs (which I was comparing to Tolkien, not Warhammer) had been defeated yet again by the other races on one of their repeated crusades of pillaging and plunder. 

Unlike preyed upon Africans the thought was that the orcs put themselves in their position of indentured servitude through their constant warmongering.  This allows for higher minded characters to question the wisdom of the deplorable situation and maybe seek an alternative solution.

One must have evil to tell a story of good conquering evil.