ESD Protection Diode: I/O Protection on VBUS Line instead?
USB is positive signal voltages only. Vcc maybe On or OFF depending on the controller but it is positive if ON. TVS (Transzorbs) are bi-directional and meant for very short transients of either polarity.
Zeners are often better when signals and power are of a single polarity. Zener diodes are built with more junction mass to tolerate more than just surges, they can clamp continuous over-voltages as long as current is limited. Also the reverse clamp is less than -1 volt and forward clamp should be close to 5 volts, though for some head room a 6 volt clamp is common. TVS diodes have the same clamp voltage in both directions, exposing the IC pins to as much as -6 volts.
To protect power the zener should be more beefy. There is no capacitive loading issue on power feeds so a dedicated SMD zener of 5.1 volts to 6.2 volts can be used. On the data lines you need to use ultra-low capacitance TVS diodes or zeners, or you will not get USB 3.0 full speed to work.