All under the greater good are equal, but some are more equal than others.[/animalfarm]
They don't use cannon fodder, and the Tau Commander will try to minimize the casualties of his auxiliaries, because wasting resources is counterproductive to the Greater Good. But there's also the fact that the Tau recruit so many specialist auxiliaries precisely so they'll always have a 'first line' that's perfect for the task at hand and not need to risk Tau lives right off the bat.