Indeed. There are just a handful of them, all males. The majority live in one of the Vistani's more permanent camps. It's unlikely most Barovians have ever seen one.Considering the average Barovians take on Demihumans in general and the fact that the total population of Barovia is approx 3,000, the actual volume of Dusk Elves would be negligible.
My understanding is that they are just wood elves with slightly darker coloring. And there are no females because Strahd killed them all to stop them procreating. I could be wrong about all that, though.