It occurs to me that Mr. House is another retcon. Mr. House says in New Vegas that he predicted the Great War was inevitable about a decade ahead of time (with his prediction being off by two years), which still holds true if this conspiracy was shortly before the war. However, if Mr. House was a co-conspirator then he intended to kill off everyone on the surface too. But House had planned on having a comprehensive laser defense system to protect New Vegas, which the platinum chip was only 20 hours too early to fully bring online. Why would Mr. House agree to be party to the conspiracy when he already intended to save the Mojave from nuclear devastation? He could have potentially saved parts of California and Arizona as well.
That's also another big flaw with Vault-Tec's whole plan. They basically have no way to control any of their co-conspirators, so if they plan on saving a bunch of people that aren't in the Vault-Tec gameplan then they have no way to stop it.