Nothing in the document prohibits an employee from gettin' down with the host. In fact, the document -- which we're told was first distributed approximately five years ago -- does not prohibit sexual liaisons in the office, provided they're not "unsolicited and unwelcome."
The policy does make it clear it's inappropriate for a supervisor to offer a promotion, salary increase or any other type of bonus in exchange for "providing any form of sexual favor to or dating a supervisor."
If Letterman were held to CBS policies, he would have been required to notify a member of the CBS brass and declare his affair. But Letterman is not a CBS employee so that rule doesn't apply.
So ... as long as Letterman didn't reward his office "partners" with perks ... WWP would have no issues with him.