Yes, when I said "make a contract", I forgot to mention the contract is established after they attune to the remnant aether or an aspected aether in a specific region, almost juxtaposed to an aether node of the land (For that matter, SMN make a contract with Ifrit in a fire aspected aether region like Thanalan - and not because Thanalan is the home of Amaljaa and their deity though it must help Ifrit has already been summoned in the region, Garuda in Gridania (wind/thunder aspected aether region) and so on, exception made for Bahamut trance, since for this one a SMN has to attune to Bahamut's specific aether and the stronger remnant of this aether is in Carteneau's field). But whether the SMN has his soul crystal or not (since it's basically a shortcut to learn skills faster or to impregnate your own fighting memories into the crystal), the SMN must be able to recall the egi with his/her own aether indeed.
Concerning the BLM/WHM, it's true the elementals regulate conjury and white magic (only authorized to padjals and the WoL or some other exception given your own rp story) but I still don't have any clue to why they're able to return aether to the land after casting spell... I can imagine why you deplete the land of its aether in the case of the BLM, since logically speaking, you take surrounding aether to form a spell or enhance your own aether and cast/launch a spell, but it would basically be just moving aether like creating underdense regions of aether (source of the casting) and overdense regions of aether (target of the spell)... if anyone has a thought to share about this I'm all ears
