Originally posted by FreshestSliceWindu in his fight with Sidious used Vaapad to a level he had never used before as a result of his emotional state, he won't be able to pull that off against Caedus.
Vaapad uses your inner darkness, so as long as he has a substantial amount, and he does, he will be no less drawn into it. And as long as Caedus is using Dark Side powers, Vaapad can channel it, much more efficiently than with Palpatine considering how much weaker Caedus is.