"Vampire" is not a species. Malack being a lizardman or a Youan-ti (sp?) or something else was endlessly debated in the forums for pretty much the entirety of Malack's run, and it never made one bit of difference to the plot. The assertion that "knowing what MitD's species is will be required for the reader to follow the story" is simply, nonesense.
Yes, some character's species are very relevant: dwarves and black dragons, the first due to Loki's wager, the second due to V's spell. But extrapolating from two instances to "therefore, every character's species is so crucial that we must be able to recognise the species on sight" is, way, way, way overreading those two specific cases.
Grey Wolf