Sorry I disapeared from this thread, guys.
I really like adwyn's idea of the zombies being WWI German soldiers. The motivation for having the Nazis in Barovia is a good one that makes historical sense. I'm also thinking of adding a Gestapo/Thule Society NPC that is looking to recover the Sunsword, the Tome of Strahd and the Holy Symbol of Ravenkind for the Third Reich's own nefarious purposes. (so yeah, keep 'em as a throwback to an ancient time).
As for getting the NPCs to Barovia, I'm thinking of having the meet on the Orient Express and becoming trapped for some reason for the night.
I think I'll allow any Thrilling Tales AdC that isn't "over the top" - no Rocket Rangers or Paragons, but everything else is fair game. The Idle Rich and Scoundrel AdCs from the d20 Modern conversion of Forbidden Kingdoms would fit nicely too. I also picked up Adamant's Imperial Age Monster Hunter AdC, and that would be perfect for a Van Helsing type of PC.
I think there is great potential for some sort of conflict between the Nazis and the gypsies, but I'm not sure what that would be yet.
I think the PCs (and major new NPCs, like the Nazi Gestapo agent) will have to be statted out to match up with Strahd. (maybe even pre-generated archetypes? - this will probably be a one-shot anyway, like a late night horror movie).