Of course, those things are never apply to grand personages.
Update: I have no idea whether or not this Viacom Global Business Practices handbook is either current or applicable to Letterman (he might well be an independent contractor (or "supplier") through his production company. But just as a glimpse into the type of apparatus giant, multinational corporations erect to govern the conduct of employees, click on the link and scroll to page 24:
"Viacom recognizes that consenting romantic or sexual relationships may develop between a manager and a subordinate. these relationships frequently lead to complications for the parties involved as well as for others in the workplace. that is why, if a consenting romantic or sexual relationship develops between a subordinate and someone senior to him or her, Viacom requires the more senior person to promptly disclose this information to his or her company’s Human Resources Department."
My guess is that Viacom has some similar verbiage attached to dealings with their outside contractors.