I don't know what you mean by aerial servant but summon monster IV would summon a medium elemental from the bestiary listed under the Elemental entry.
So yes, an air, water, fire, or earth kind of elemental.
By RAI, just Air, Earth, Fire and Water elementals.
Also the medium elementals you get with SM4 is CR 3 and the aerial servant is CR 11, how would this ever be balanced?
The CR equivalent of the aeerial servant would be the Elder elemental, which is summoned via SM8. At that point, it would be something you could ask your GM to houserule, but by RAW it still doesn't work.
By RAI, just Air, Earth, Fire and Water elementals.
I don't see any issues with any of the other bestiary elementals, since the ones called out by size in a way to make them valid summon targets are all at the same CR as the original 4. While the PDT obviously didn't know all the details of new elementals in unreleased books when the put out the CRB, it does seem like they've tried to keep elementals that are divided into small/medium/large/huge/greater/elder tiers reasonably balanced with each other, possibly on the assumption that Summon Monster applies (it certainly does by RAW).
Granted, the Aether Elemental in Bestiary 5 might be a bit under-CRed. Permanent unremovable Greater Invisibility can be real nasty to any opponent who doesn't have a hard counter for it.
By RAI, just Air, Earth, Fire and Water elementals.I don't see any issues with any of the other bestiary elementals,...
Yeah, I think I'm going with [citation needed] here.
SKR on summoning other elementals
If you want a different answer, you could FAQ it here.
SKR on summoning other elementals
If you want a different answer, you could FAQ it here.
Thank you.