They're both vampires in Fate, and that's about it. She calls him 'Uncle Vlad' and he allows it. The historical Elizabeth Bathory and Vlad Tepes III not only lived in entirely different countries but lived roughly 100 to 200 years apart.
Also she recruits him to do the costume stitching, because as a Lancer he has mastery over all things lance-shaped, and needles are tiny lances, ergo he is an expert seamstress. Yes, really.