Anthy has a persona in every house. Akio is clearly an instructor for Slytherin, and awards points based purely on attraction, regardless of house.

Oh dear, now I'm sorting all of Utena's characters into their respective houses in my head. Miki is definitely Ravenclaw, although I suspect Kozue is Slytherin. Miki probably didn't take it very well when the Sorting Hat separated them immediately upon arrival.