Near as I can tell they do steal stuff, but they do it so infrequently that they aren't worth much. And they don't do anywhere near the dps of standard fighter pets, so there isn't any use for them.
I haven't been able to see if the crew stealing mechanic does anything either. It never seems to do anything, but I see the power being used. Honestly, I'm not sure what it's supposed to do in the first place.
If it replaces dead crew that's fine, but my crew is never dead...they just from alive to injured and almost never actually die off, so it doesn't mean anything. *shrug*
The Crew Stealing may be designed to make your opponent lose crew and replenish your injured list... However, I have tested this and it barely effects enemy crew numbers at all.
I have never noticed the swarm of them stealing anything myself which is hard to believe. What did they steal for you and under what circumstances?
I have noted that their Beam Arrays strip shields at a surprising rate.
Hmmm... I finally got a Commodity using 2 hangar fulls of these things. They are decent shield killers and more effective in general than To'Duj but their special stealing ability seems to be exceedingly rare.
In my first day of using the advanced slavers, I got 32 contraband. That was from three STFs and the four Empire Defense dailies. That's it. They've also stolen plenty of lesser commodities that I just immediately recycled so I never saw the total amount on most of those, but it was pretty decent. I did keep the 15 medical supplies they stole since they're fairly useful for DOff missions. They aren't very good at stealing ECs though, as they only ever stole 300-400 ECs & did so infrequently at that.
If you're running slavers for their ability to steal, it's worth running two hangars. I run two & have my Vo'quv fit with pure torps & mines, and the damage has been good as long as I can keep my target in my forward arc. Aux to Damp and Grav Well keep smaller targets in front of me, and anything too big for Grav Well to affect is generally too slow to move out of my firing arc anyway.