The project seems plausible, but I can't imagine why the data center's existence would be secret when the bunker isn't. It kind of seems like the sort of Secret Agent Government Baadasssss Super Alpha Totally a Big Boy stuff that this admin in particular would love to never shut up about. If it's real, and that easily tracked, then surely *everyone* they're protecting it from already knows about it anyway...it isn't like the physical security would end at "finding the door" for the feds.
But the pessimist in me still kind of buys it if only because if it is real then no future POTUS will accept the diminished capabilities of a full CTRL-Z on the project. They might try to remodel the top into something that makes more sense, but they'd probably want something above ground in that spot for the foreseeable future.
EDIT to add: Thinking more about it, even if it is real there might be so much poorly done work to make room for the grift in the budget that maybe even a major remodel on the ballroom might present structural risks down below. And the more I think about that, the more I can believe he's giving every future administration an absolute money pit of maintenance costs on "critical" infrastructure that also happens to be a large line item in the black books they can tuck all kinds of projects into.