Does Lulu's ultimate affect health scaling damage?

Does Lulu's ultimate affect health scaling damage such as Bloodrazor, Fizz's Seastone trident, Vaynes silver bolts, etc?

Any effect that scales off of maximum health takes the current health maximum of the champion. This counts for on-hit procs (bloodrazor) as well as targeted abilities (Fizz's trident) and AoE abilities (Xin Zhao's ult, assuming it's levied against someone who is currently at their max health).

Those abilities take into account items granting permanent health, items granting temporary health (red elixir, for instance), and, yes, Lulu's ultimate.

While it should go without saying, anything that adds a shield, but not health doesn't increase the calculation for maximum HP. This design choice allows the developers to change the power level of abilities and items in a more granular manner.

It will affect them yes. you get more %hp during the ultimate so you will take more damage from such items in return.

Of course, for as long as the buffed character has improved HP, the numbers on HP% damage items will be altered.

If you are referring to how the champion with the ulti is affected then yes.

I would believe that it would react to %hp items and skills.