I would guess that that usually works, but isn't guaranteed. On the whole, BtS worldbuilders are identical in format to vanilla and Warlords worldbuilders - except of course that there are lots of extra things that can be referred to in BtS that wouldn't be recognized in vanilla or Warlords. However there may be some things that have changed rather than been added to (offhand, I think the representation in worldbuilder of the name of one of the Chinese leaders changed at some point), so it's possible that kind of thing might prevent BtS reading some worldbuilders without tweaking the worldbuilder in notepad first.
But I'm glad to see in general this works - could give a whole new lease of life to some of the older games that I'm sure many of us fondly remember playing.