Maybe they could build nuclear but they could just as easily build solar with battery backup or natural gas. Lots of industrial facilities have natural gas cogeneration with the grid as a backup. If you can't get a grid connection at all due to permitting, you could just forego the backup. The reliability wouldn't be as good, but in a distributed datacenter there are ways of building in fault tolerance.

If these guys really have $500 billion, they're going to find a way to get electricity.