The Damocles Anthology covers them in one of its stories. They are given a pulse rifle and armor that is "actual armor" as one of them puts it. They were sent as envoys along with the water-caste to first try and sway the opinion of one of the hive governors on Argellan. When that failed, they entered combat alongside their tau superiors against the local guard regiments.
As for vehicles, there weren't any outside of Tau provided transportation which might be because the tau