Socrates200X, a programmer working on Fallout 3, has this image hidden away on his website. It looks like a book-cover, and features the text "So you've become a vampire", "Introducing you to your new un-life" and "Tenpenny Press". Moreover, it also features an image of a vampire with a striking resemblance to Vault-Boy.
A close look at the vampire:
The original Vault-boy:
While the resemblance is striking, I doubt that we can make any conclusions based on this picture.
EDIT: The site became unavailable only minutes after I posted this story, and now only features a Geocities error message which proclaims that it has "temporarily exceeded its data transfer limit".The message appears to be genuine, and Geocities does have a very low bandwidth limit. The original image can now be found here.