So basically it's the same with T'au drones and other forms of AI. They are programmed to serve the T'au'va and to regard themselves as fellow citizens in the Greater Good.
The T'au do place restrictions on their AI. After some incidents, the T'au tinkered with drones' thinking processes to be less coldly logical and mimic the T'au.
Furthermore, the T'au forbid self-replicating machines
While machines can be corrupted, it's harder to do so than with organic lifeforms. It takes certain rites, long-term exposure, or an encounter with the dark demigod of technology for that to happen.
Some AIs have shown incredible resistance to Chaos. The DAoT AI, Tabula Myriad, was immune to Chaos corruption because of its mathematically ordered mind.
Going by what I read from the Farsight and Shadowsun's novel, the T'au don't treat sentient advanced drones like pets but more like people. They even mourn their "deaths".
Arch? Yikes!
The T'au and Drukhari weren't the only exceptions. During Old Night and the Great Crusade, there were human civilizations that allied and even incorporated alien species into their empire. Hell, even the Imperium did it. There is at least one example of the Great Crusade Imperium assimilating an alien race as a vassal. Horus considered doing the same with the Intrex. Lorgar was sent to the Asuryani to negotiate their place in "humanity's" galaxy.
It's the opposite. Judging by how the T'au are faring Chalnath Expanse, they are dealing with the GSC infestation way better than the Imperium. The T'au Empire is better run, more ordered, and much more observant than the Imperium. The forces of Chaos and GSC find it hard to hide and thrive in the content and ordered societies of the T'au worlds. The GSC and Chaos forces that the T'au encounter mostly come from Imperial worlds they are invading and assimilating. So they are cleaning up the Imperial messes.