At all of the companies where I have worked, the rule was only about direct subordinates. That means you can date your boss two levels above! If practice, if you started dating your immediate supervisor, HR would just change your supervisor. Literally, this has been explained to me multiple times during HR onboarding.

That said, Kimberly Powell (former Vice President of Healthcare at Nvidia), reported directly to Jensen Huang. That is a big no-no, probably enough to be demoted and/or fired, especially as CEO.