So, the general consensus is...don't zeta Vader solely for raid damage as that may or may not continue. I'm in the boat of farming my first zeta and was considering putting it on Vader for that reason alone. I don't even have Kylo yet, but him or Barriss would help my squad in more areas of the game if I used it on them.
After reading this thread, I am unsure. I would be the first in our guild to do so and we only run T5 right now. We are going to start t6 after the palpatine event. At 12 mats, I should be close to my first by then. I doubt I would run him as my arena leader, so maybe I will hold off. I have a pretty decent Teebo team.