The rules, in this case are pretty clear. The spell never mentions mirrors or reflections, it “summons illusory duplicates." Spell names aren’t indicative of their mechanical effect. See Chill Touch.
There’s also vampire wizard statblock that has Mirror Image on its spell list.
It would be funny if the spell just failed though.
I'm pretty sure that the rules as intended for this one are that it just affects attacks, I'm afraid. Sage Advice repeatedly argues that the intention of wordings like this is that they don't extend to other effects.
Of course, it's perfectly fine to run your table different to sage advice. There's a lot of stuff in there that I think is rather silly, or bad design.
Were you able to see the whole space, you should be able to see the illusory duplicates fine (they're not "vampires" mechanically), but not the real vampire, so I'm in full agreement there.