User blog comment:Emptylord/Archived/PBE Patch Notes (Preseason 3)/@comment-4083774-20121128214007/@comment-5490997-20121129092205

I personally doubt either of those will add damage multiple times even if you kill multiple things, I mean it never worked with the old Tiamat, right? I think the main reason this is true is because Nasus's Q doesn't apply on the AoE and his Q is the only thing that increases the damage of it. Basically the entire AoE is a regular auto attack or another form of damage, but as we all know Nasus doesn't gain any damage from just regular auto attacks or random sources of damage.

It might be worth testing, but I personally would be surprised if Tiamat/Hydra/Iceborn allow faster increases of damage with less mana cost as well.