As per the discussion about setting during last night's game:
The original Ravenloft module was released in 1983. This was just an adventure where the characters fight the vampire lord Strahd in his castle. The boxed set campaign setting was released in 1990. I can bring the box set to the next game session if anybody wants to see it.
The first version of Castlevania was released in Japan in 1986 and in the US in 1987. There doesn't seem to be any reason to suspect the original Ravenloft module was an influence on Castlevania, though. I'm not sure what the state of D&D in Japan in 86 was, either. I've heard that games with weird dice were much less popular in Japan, and D&D was re-written to just use six-sided dice.