Ok so I'll be honest, this is another double Deffender list. Unusually for me though, there is a plan here for how each ship will act and even a tiny bit of synergy...

Tie Deffender - Colonel Vessery + tie/d + ion cannon + Adaptability + twin ion engine mk2

Tie Deffender - Countess Ryad + tie/x7 + veteran instincts + twin ion engine mk2

Lambda shuttle - omicron pilot + Darth Vader + ST 321

So, obviously the shuttle hangs back keeping out of the fight and locks Vesserys target.

Vessery, hopefully with a focus, ions and then primary weapons the first target. After this he moves on to the next target leaving the first for the countess to finish seeing as, with her crazy movement options, she should be able to get/keep it in arch knowing that it's next movement is going to be a 1 forward.

The shuttle can watch the Deffenders backs and then come in to its own later in the game, Vadering ships that are down to their last couple hull points.

I know from experience that most plans don't survive contact with the enemy but is this viable?

I've played teh Doom Shuttle quite a bit and have learned that you don't want to keep the shuttle out of the fight for more than a round, two at the more. The extra damage that is can deal with just 3 red dice plus Vader is significant. If you have a bad roll with one of your defenders, you don't want to get left with a single defender and a shuttle.

Maybe slow roll the shuttle on turn on, continue with 1-straight\banks and lob dice from afar. Just don't wait to long. Without Palp, most people will ignore it for the first couple turns.