If you've got physical access to the machine in the cage you can do anything you want, which includes bypassing BIOS and Bootloader passwords in about 5 minutes.
That assumes you have unlimited physical access. 5 minutes per machine * 80 in a rack * 1,000+ racks is a real world limitation.
PS: The NSA has a vary different approach to security than the average firm. To put this in perspective they have been known to refer to their computing power not by computer or rack but by the Acre.