Are there any sources in Judaism that discuss vampires? I am aware that it is mentioned in the sefer hassidim but have not found any other source material. I am specifically curious if there are any sources that connect it to the metzitzah process during bris milah but I'd be happy with any sources that discuss vampires in general.
This article briefly touches on this subject; the only real substantial additional source she sites is the Seforno to Vayikra 17:4 (though she probably means 17:7, who was prceeded by Rabbeinu Bachya [ben asher] on Dvarim 12:23). Unsourced are claims by Rabbi Menachem Zioni that vampires were associated with migdal bavel and a broad proclamation that according to many kabbalistic leaders there are parallels of these creatures [vampires and werewolves] in Judaism.
Much of what she writes seems to be based on this short piecepublished in the Jewish Free Press in 2001 which in turn cites Dan, Joseph. The Esoteric Theology of Ashkenazi Hasidism. Jerusalem: Mosad Bialik, 1968. which I'm guessing is based heavily on the Sefer Hassidim you reference and Trachtenberg, Joshua. Jewish Magic and Superstition: A Study in Folk Religion, Temple Books. New York: Atheneum, 1970 but gives no page numbers.
A further study of that latter source reveals references to Rokeaḥ 316 and some additional recent scholarship. Sorry, nothing related to bris milah that I could see.