Vader Crew - After you perform an attack against an enemy ship, you may suffer 2 damage to cause that ship to suffer 1 critical damage.

The FAQ says:

Stealth Device

A ship equipped with Stealth Device only discards

Stealth Device if it defends against an attack and is hit.

Damage suffered from other game effects (such as

Seismic Charge, asteroids, Feedback Array, or damage

received for being at Range 1 of a ship hit by Assault

Missiles) does not cause a ship to discard Stealth Device

So based off this I would say that Vader's ability would not take away Stealth Device.

Is this correct?

Correct, vader does not remove SD if the attack did not hit.

There are many things in the game that could cause a ship to suffer damage and not remove a Stealth Device. Darth Vader crew is one of them as are bombs and the splash effects of some attacks on other ships. Incidentally a Stealth Device can be remove in a couple ways even if a ship suffers no damage from an attack; Lt. Blount always "hits" which removes the SD even if he doesn't deal any damage and the Tractor Beam can also "hit" which removes the SD even if all dice results are cancelled before damage is dealt.

Played a game with Soontir, and Ties against Oicunn with Vader, Lt. Colzet. and Zeta Leader

Vader put a Major Explosion crit on Soontir. I rolled a blank and turned it over.

Colzet flipped it over at the end of the round and I rolled again, this time getting a hit forcing me to take another damage.

Next round got another crit from Vader and died, having never lost my stealth device.

Managed to put 3 damage each on Colzet and Zeta with Soontir before I died, but it was the most frustrating thing ever.

Ended with my ties killing Colzet, getting Oicunn down to 6 hull and Zeta flying around with only 1 hull, so lost 122-78.

What about Oicunn bump?

What about Oicunn bump?

Also not a hit.

Unless someone is actually making an attack and actually hitting with it (i.e. either having more uncancelled [boom] and [kaboom] results than evade results, or being Lt. Blount) Stealth Device stays intact.

Correct, vader does not remove SD if the attack did not hit.

Wow, I got played... R.I.P. my Soontir last weekend.

Quite obviously my fault for not knowing the rules, but I also thought (and was not corrected by my opponent ) that the crit from Vader was slid in under shields - which apparently it's not.

Correct, vader does not remove SD if the attack did not hit.

Wow, I got played... R.I.P. my Soontir last weekend.

Quite obviously my fault for not knowing the rules, but I also thought (and was not corrected by my opponent ) that the crit from Vader was slid in under shields - which apparently it's not.

Card effects will specifically say "a face-up damage card" if it's expected to bypass the shields. If it just says "a damage" or "a critical damage", shields will still absorb them first. Subtle difference, and you're neither the first, nor I suspect the last, person to misunderstand the cards.