Depends on who you're asking. In the minds of writers who write vampire stories, yes, they do exist. They share their various encounters with them and those experiences of others who have had the pleasure and good fortune to be in the company of any of their kind. Bram Stoker was the first to "come out of the closet" with his tale of the father of vampires, "Dracula." Since then many more have done likewise in spite of fears of ostracization and disbelief on the part of their readership.
Hopefully this helps.