FFG had a missed opportunity. They should have Vader discard officer cards to have him trigger his ability. Or bring up an additional commander and discard that commander to do something cool.
This won't work, and I'm glad they didn't do it this way. Just stop and consider the list-building ramifications of this... not only are you paying for Vader, but you're paying for the officers to kill just to kick his ability. Plus think about every other Admiral in the game... all of their abilities are constant. Vader works only if you buy all the officers for him to kill, and place them on every ship in your fleet. He would be useless for any list that didn't put officers on those ships. It makes him less worth it than Motti.
Vader's current ability is thematic. Vader squeezes out success at the expense of defenses. By making ships and equipment weaker on the drive to victory he is treating the fleet as expendable. Works for me.