The Tavern

Thematically it fits as you curse the creature to be hanted by ghosts. (Necromancy covers the summoning element already as it's a part of necromancy to raise the dead from the grave.)

Hexes needs some more spells, summoning has enough.

Necromancy and hexes seem like a natural fit as both deal with the dark arts. (witches practiced necromancy and curses.)

What if haunt were replaced by a combination of two spells, modeled on control teleport and teleport self?

The spells might be "Haunt" and "Summon Phantom."

Haunt would be level 6 Necromancy/Hexes, and "Summon Phantom" would be level 5 Summoning/Necromancy. Haunt would smite target a single enemy, and all [your?] summons would appear near the haunted enemy until another enemy (or the player!) is haunted. It would run out after a time dependent on spell power.

Summon Phantom would call up the baddies that Haunt calls now and put them in the standard place.

Air-dropping a ghost army is a pretty overt effect for hexes, and Haunt is a pretty darn fine summons as is. I don't much like the idea that non-summoning spells should be better for summoning than actual dedicated summoning-skill spells, so if Haunt was made non-summoning it seems to me like it wouldn't be able to stay much like the current implementation. At which point there's no longer any benefit to moving it over.

Moving the cloud spells to hexes is a different sort of change. The cloud spells don't really have much in common with the other conjurations, so there's not really much more than precedent keeping them in place. Haunt is almost exactly what you'd expect a summoning spell to be like, and the only major difference between it and the other summoning spells is an extra advantage it has. At the moment, non-summoning minion creation spells all have a reagent cost that keeps them under control, so that they are never strictly better than a summoner's summons.

I don't know that I like this reasoning - if that were true, then wouldn't Animate Dead, Animate Skeleton *also* be Summoning?

I say leave Haunt as it is.