Vader should win, it's just that his history doesn't reflect anything of the sort and he has a tendency to ignore his usually massive power advantage. The CIS is so common now that it's hard to make an argument for him actually using his power advantage.
As he tends to be written, no, Vader won't win. But if he's ever written properly, he should be able to trump these two - Ventress is several orders of magnitude below him in raw power and physicality, nor is she as skilled with a blade or as masterful with the Force. And Vader's basically a better version of Maul, in virtually all respects.
Thing is Vader is never written, at least to my knowledge, to lose due to a failure to abuse his Force powers. His failure to do so only seems to happen we he doesn't really need to.
Given that I don't see Vader losing without first using all the powers he has at his disposal, and under those circumstances Ventress will get destroyed.