ESD diode selection based on VCC of the IC
Normally you don't need ESD protection on the supplies (VCC) of a chip!

Reason: there should be decoupling capacitors between VCC and GND. Those capacitors will "eat" the ESD pulse, I mean, an ESD pulse does not have enough energy to significantly charge the supply decoupling capacitors.

Also: all ICs have build-in supply clamps as part of their ESD protection, these clamps are capable of handling the current from ESD events. ICs need these clamps as a positive ESD pulse on any input will be routed to the supply (VCC) rail by the ESD diodes in the chip. Without that clamp the VCC could increase too much (if there are no decoupling capacitors connected, for example when the IC isn't soldered on a PCB yet) and damage the IC. To prevent damage, the supply clamp(s) (most ICs have several) short the supply in an ESD event. How I know this: I have designed the on-chip ESD protection of some ICs.

So in my opinion: there is no need for VCC ESD diodes assuming you already have supply decoupling capacitors. If you don't have supply decoupling capacitors then please explain  why you don't have them.