I'd like to think there was one creator/definitive producer (even if it was the mind who just said, "hey, let's do a Dracula game!"), and given IGA's response it hints at one person.
Akihiro Nagata is listed as the Producer and Game Designer of Vampire Killer, but I can't find him on any other MSX1/2 game credits to see if he was busy on those platforms with other games.
Interestingly, Metal Gear on MSX2 (07.07.1987), like Vampire Killer, has a Game Designer entry listing Hideo Kojima. The NES version which came later (22.12.1987) has no such entry, nor even a Special Thanks to Kojima.
The NES version Maze of Galious, which I believe shipped well after its superior MSX counterpart, lists a completely different staff team from the MSX version, although they nod with a Special Thanks to Ryouhei Shogaki, Graphic Designer and Planner/Director of the MSX version.
It's rather here-or-there if you were to take any stock in that kind of thing. With Vampire Killer, given the release dates, there's not much in it:
26 Sept 1986 Akumajo Dracula (Castlevania) - Famicom Disk System
30 Oct 1986 Akumajo Dracula (Vampire Killer) - MSX 2
(Source: msx.org)
But who can truly say which was programmed first? Also, the Special Thanks nod to the FC Team could have been in relation to anything; i.e. help with disk to cartridge (although unlikely). And while it seems more logical to suggest different platform teams would share the same producer, there's no real evidence to suggest this would be the case, given that teams appear to be "platform-specific".