1. From what I've seen any SMN type demon summons these things.
I.E. Judicator, Abyssal etc.
2. The elemental summoned is not limited to the elementals found in Xarcabard.
I had a coffer key party in Castle Zvahls earlier and the Demon summoned a thunder elemental during ice weather.
I have a screenshot of it and I'll send it in as soon as the server maintenance is over.