ALL droids don't, though many elites (esp in flashpoints) do have the same passive stealth detection as bosses.
The pack mentioned by the OP in Hammer Station has a pair of gold star droids that WILL spot a player in stealth long before they get in proximity agro range, WILL engage the group in combat if the player in stealth does not immediately drop stealth, and WILL switch agro to a healer if they happen to be casting heals.
While it isn't clear exactly what happened, listening to the OP go on and on about how much they know about stealth while clearly demonstrating they did NOT notice the pair of droids in that particular pull having the passive stealth detection / auto agro ability leads me to believe the group kicked the OP for pulling.
All I've got is anecdotal evidence here that says that every time I've stealthed near a non-boss non-stealth scanning droid in an FP or operation (for sleep dart purposes usually), I've never been knocked out of stealth without any warning.
The passive stealth detection bosses have ALWAYS gives you a warning before popping you out of stealth, and your entire group can see it too. I have never EVER seen a non-boss cause that warning. Maybe that one pull in Hammer Station is a fluke (probably only done it once with my Operative), but I really doubt there are mobs with boss-level stealth detection that don't give you the warning debuff.