> I don't think the Tau will see much gain to be had from madness.
They don't yet, but they generally haven't had to deal with a full blown chaos incursion yet. Remember, the Ethereal caste is quite happy to sacrifice the odd Tau for the Greater Good - see the railgun snipers and their unfortunate tendency to die from feedback. Those who created the Outreach program know (or at least have an inkling) that there are hazards out there which cannot be combated in normal ways. They need Tau who can understand these hazards. Unfortunately, in trying to understand these hazards, many go potty. A lot of things in Warhammer 40,000 simply don't make much sense, especially if you try and approach them from a rational, scientific point of view. The ethereals may have realised that they need to approach the problem from a different point of view. Look at the Imperium - from the outside it appears to be a cult made up of violent lunatics, but time and time again they hold back terrible chaos threats. The Ethereals know about chaos, even if they don't really tell the rest of the Tau. Given that the Outreach program is taking a slightly different approach to normal Tau philosophy they may be more willing to allow "deviant" philosophies in their, for want of a better word, acolytes. If it works, it works. The important thing is that the threat gets neutralised. They can always have a sane member of staff go over the data later to look for more rational explainations.
Remember also Tau madness might not take the same shape as human madness. It could appear as obsessive devotion to a cause, for instance. It may not appear to be a problem until too late, especially if the Tau in question is away on operations a lot of the time.