The old codex used to have them, called something like Tau Auxiliaries or some such. They fazed them out in the newest codex.... But, if I remember correctly, if you use them as normal Tau warriors, you can model them that way and just say that they are fluff-wise gue'vessa, but game terms regular warriors (or kroot if you wanted)
A tiny portion of humanity turned its back on mankind in the waning days of the last Golden Age. Over one and a half centuries later, the PHR has emerged from the shadows as an unrecognisable civilisation, its people irrevocably changed. They are no longer simple human beings, they are post-humans - cyborgs.