i'd say it doesen't work correctly.
as i'm not using 8th brother at all with the other inquisitors, i tried to get the feat in sector 2, by using his unique. "... if he had stealth during at the beginning of the turn... , he inflicts 1 stack of purge ... by that ability".
i ran jkl, jml, wat, chewpio, 8th brother (team for getting blinds vs jedi in sec 5) vs rex clones at the datacron node in sector 2. started with 261 purges, inflicted a few purges and even made a picture of a clone who had purge on him, and in the end when i checked it was still at 261.
i guess it doesn't count, because it's in 8th unique. on the other hand it is worded that he inflicts purge by (!) the basic or 2nd special ability if he was under stealth.