Couple of things.
The Winter Voices files are dslibrary files rather than dspreset file; I think only dspresets are currently scanned and added when you open Decent Sampler
Are you trying to load via FILE… or via BROWSE/My Libraries ?
Use FILE, select Load and find a .dslibrary and try it.
Next time, go to BROWSE then My Libraries and it will have been added to that list.