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.