I do know that nyx, Tartarus and Erebus are in House of Hades and are all primordials like Gaia however Erebus is dead at that point however the advantage of AU is he could still be alive. Erebus is the primordial of darkness and Nyx's husband in Greek Mythology.

Since you mentioned Tartarus will this possiblity be a percy jackson universe crossover since it is technically a DxD au. It could be cool to see Kane chronicle characters etc. . Just asking will still be following regardless.