Surely the whole point of vampires is that they are unalive. They don't just 'lack' a circulatory system; they actually do possess one, it's just literally dead and non-functioning. It's the whole reason they need to drink blood to sustain themselves. It's a completely different kettle of fish from a living being which evolved without a blood circulatory system; a jellyfish is a living being that evolved in such a way and in such a setting that it doesn't need a circulatory system to live, a vampire is a dead being with a dead circulatory system that can for some quasi-magical reason still hold a conversation.

There may indeed be ethical dilemmas to killing vampires, but trying to argue that they're not actually dead (at least, in their classical forms -- which this depiction clearly is) seems a bit questionable one.