Unless they promised to give him a large sum / stocks after everything is settled if he agrees not to talk.
Nor is the judiciary powerless against attempts to exploit loopholes, if they indeed exist.
"Muahahaha! The law is powerless against me and I can violate it with impunity by judicious word choice" is largely a fantasy.
This "law hack" would be immediately caught by Waymo and Judge Alsop would rightfully penalize Uber. The corporate officers who signed off on an action like that would likely be criminally liable as well.
The problem is, how do you differentiate between equity whose grant is meant to manipulate a party of a crime and equity justly earned by working there?
If I were Uber, I would fire him and if possible, revoke any equity he had to absolve the company from any accusations of implied manipulation.