Speculation:

Hades could be the black ooze killer, Hades could also be the leader of a pro-Hades cult.

I honestly don't know, though. I've been baffled by Netherworld setups ever since the last one. I'm not too good with the mythology and I can't predict what goes on inside Khaan's unique mind.

I would think if the black ooze killer is opposed to the Hades cult, if any, the Hades cult should reveal one cultist now so we can destroy the Black Ooze Killer.

They would have information we don't have and point us at their top suspects.

That said, I am not certain their info is trustworthy either. I'd only listen if they could offer proof of their claims, evidence which we can see.