Yeah, using the Orks as a weapon would be considered very morally borderline by the Culture. But 'uplifting' them to give them more mental flexibility is very possible. From the Culture's point of view the Orks 'almost' have free will but their creators restricted it so that every choice they make must in some way involve fighting. Removing that restriction would then be 'freeing' the Orks from a form of genetically enforced slavery that persists long after their masters death.