No the Tau are very utilitarian
Preference utilitarianism is a particular type of utilitarianism which defines the good to be maximized as the fulfillment of persons' preferences. Like any utilitarian theory, preference utilitarianism claims that the right thing to do is that which produces the best consequences; when defined in terms of preference satisfaction, the best consequences can include things other than pure hedonism, like reputation or rationality.
Note that for sake of argument I'm using only one of the forms described, although there is evidence for that extreme end of the spectrum of utilitarianism of people dying for the greater good (aha!) in the Tau, reference "For the Emperor", Black Library.
Of the two, the Tau lean far more toward the utilitarian philosophy, for the following reasons:
1) They did not have a period before the current ideology of exploitation by a ruling class of those less well off than them.
2) Their society is not "classless" as a rule. IT kind of is, but isnt. There are differing ranks within the castes (La, Ui, Vre, El, O) , which can correspond to classes (upper, middle,lower). In this way it compares to meritocracy, assuming promotion is based on skill rather than connections, the former of which makes more sense for the Tau.
3) The greater good is an even more succinct version of the definition. The greatest good for the greatest number, in this case, in the Tau empire.