What it says on the tin. I don't recall if anything's been said one way or the other in canon about this*, but now that we've learned how to undo tempering in others by basically resetting their elemental aether balance, are we in general agreement that that's what happened with Hades at the end of our fight? He was the "darkness to your light", as Y'shtola puts it; which implies the reverse is true as well. And, in the end, he could say "remember us" with a smile on his face and actually let go of his mission, which I don't think he could have done if tempered.
EDIT: Further thought - When Elidibus says "Would that I had been there to offer correction" regarding Hades' change of heart in the end, by "offer correction" could he mean re-temper him? Given his role as Zodiark's heart, theoretically he could have done that. Though maybe not, cus if he could temper people at will, you'd think he'd do so. SO I dunno. Just speculating.
EDIT 2: I also don't think Hades could have helped us fight Elidibus if he was still tempered. Though to be fair, the exact nature of what came to help us is still a question, so I'm not sure if it counts as evidence at the moment.
*(I do feel like this is something that may have been discussed in-game and I'm just not remembering it, so please don't hesitate to just cite at me if I'm wrong.)