I think you guys overestimate the lack of knowledge the Tau have about the Warp. They know it's a thing. They don't really get what it is, but they know it's there, they know how to use it to slingshot themselves through space to get their skip drives to work, the higher-ups know exactly the nature of the threat, and my guess is that knowledge about it on the higher levels depends highly on the individuals, but...the Tau still have legends. They still have their Ethereals, and while they're a lot more...something, to have advanced so quickly in 4,000 years to this level, I think 'organized' is a better term than 'scientific'. They're past the point of believing in magic, much as humans are mostly past that point nowadays (and if you tell someone that miracles are magic, you'll get a rather negative reaction, for that reason), not because they're intrinsically incapabable of attributing unexplainable events to woowoo forces, but because they're the Great Crusade the Emperor wanted, except with less facepunch and more xenoslove. And also no actual Emperor. They get Ethereals instead (strangely charismatic leaders unite planet in time of strife and lead them into an unprecedented era of expansion and assimilation; Ethereals are a caste-wide version of the Emperor, diluted and more diplomatic/manipulative than intimidating/psyker). They're in that era of reason and science. I mean, a pronounced lack of Daemons probably helps that, yeah, but humans themselves are barely capable of grasping the idea of the Warp, though we can think of an approximation of it.
The Tau appropriated Imperial technology when it benefitted them, it's just that a lot of Imperial technology is remarkably inefficient, at least in the Tau's view. Until and unless they capture an STC, this will likely continue to be the case. And if they get an STC, either the Empire is in for a really good time, or a really bad one, depending on how kneejerk the Mechanicus reaction time is.
I did come up with an idea for a story in which the Tau create ansibles that their gue'la engineers look at in horror and tell them are 'machine spirit astropaths' (whatever the mon'tau that means), and have a limited range, though still massive. Relay stations get set up to create far-reaching new seed colonies to try and get Septs started outside the main spheres, as an experiment. Unfortunately, when the relay stations experience strange interference and attacks by odd beasts, despite their often deep space or otherwise isolated locations, contact is lost. Of course, most of the seed colonies die out for one reason or another, but at least one survives, the warp storm that started up and transported their sector of space to a different sector of space has finally died down, and after having expanded remarkably well, they're now desperately trying to cut a path back through the galaxy to reestablish contact with the main Tau Empire. And that's my special snowflake cadre
C'mon. Farsight is a revolutionary. Let's not be like that.
But also I'd like to believe that Tau are just as edible, they just don't warp-dive as much as warp-skip and so therefore aren't subject to the horrifying nightmares that the warp brings.
Plus they probably have some Gellar-substitute.
They...don't, really. They just don't fully enter the warp. I mean, I've read some stuff that acts like they use the psychic races they've assimilated, and they might have some sort of weak one that's built into the engine, but there's nothing canon that I really remember well. And they really aren't as tasty for Daemons. They have much less significant presences, their souls are smaller and less filling, though they'll still eat them. They're just less attractive to chaos. Though I did have headcanon for a while that Ethereals were actually Daemon or at least created by Chaos(Tzeentch, specifically...).