Either one alone would give him a challenge.
Their TK feats are over anything Novelitate has done, and iirc they have good barrier feats, which should be able to hold off Vittys lightning for a time, while the other one attacks him. Questions?
Various ins and outs between Malachor V, Nathema, and then the Star Forge. Vader hasn't got much in terms of TP resistance and the Starkiller clone too unstable - it's really not a question of whether he gets mindraped or not, he just does, and Vader's apprentice will be turned against him -- Tempest should restrict TP and I'd give it to the team.
If we consider willpower to be synonymous with telepathic resistance, then Marek and Vader's abilities to will themselves through various near death experiences should suffice here. Certainly Vader & Marek are much more powerful than Revan and Malak were.
I'm mobile at the moment, but the effectiveness of Vitiate's mindhaxx in this scenario begs for proof. The Revan novel indicates that it takes a considerable amount of effort from Vitiate to make an attempt. The SWTOR Encyclopedia mentions that Malak and Revan were easy targets because they were already on the precipice of the dark side... To say nothing of the home turf advantage and prep that Vitiate enjoyed from the trap.
If there's evidence that he can win the day via an unprepped mind hack, I've yet to see it.
Team demolishes. There no evidence to suggest Vitiate can auto mind rape someone as strong willed as Vader and Starkiller, on the fly, without prep.
Vader's will power is sufficient enough to give Chaos the finger and virtually will himself to stay alive, while Marek, shouldn't be too far behind. Once telepathy is outta the way, Vitiate gets torn a new @sshole with either frigate busting TK +, or CQC from two most skilled warriors to touch a lightsaber.