(Kinda like what the Catholic Church did for the nasty priests.)
In the case of the Catholic church, the non disclosure agreements were part of a settlement. We pay you x dollars and you drop this and any future lawsuits and agree to never disclose these allegations. Etc.
Unless Letterman already has such settlements in place, I doubt that any court would uphold a preemptive sexual harrassment settlement. The women who “slept” with him received preferrental treatment in work assignments, compared to other employees. In a sense CBS is the victim, since he made business decision to benefit himself rather than to benefit of his employer. It’s no different than if a mid level hiring manager demanded kickbacks from applicants.