DaasYochid and PBA: Without knowing too much on the matter, I believe your paradox can be solved in this way: YU Roshei Yeshiva and YU people may not believe in “Daas Torah” when it comes to non-torah related matters, but they certainly (at least, the majority who are truly “modern orthodox”, not the small minority of non-frum people trying to keep themselves called “orthodox” who make everyone else look bad) believe in daas torah (aka Psak) in halachic matters! If a YU rosh yeshiva tells his talmidim to do something halachically required, they would do so. (I have not seen that this agreement was portrayed as something everyone must do)
Side note: the prenup website also lists Rav Ovadia Yosef zt”l as being supportive of their prenup