I wonder if the opposite would be true--if someone invited Barlow in, could he then send one of his minions there? (After all, what's the point of having minions if you can't delegate things to them.)
When I taught literature, I told students that when you come up with a theory about a story or novel, you have to look at what in the text supports your theory and what in the text does not. While my theory is speculation, I don't remember anything in the text that would prohibit it. The whole "vampires have to be invited in" thing is not very spelled out.
Is there a central authority on vampire policy who decides these things?