HP's high-end 'ProLiant' kit have "Integrated Lights-out" that will allow you to do things like power cycle the device, drop on to the serial console, etc. All over a user friendly web interface.
I'm assuming this 'admin backdoor' it is for that.
It's a SAN device with a ton of drive bays. We've got a few and they seem pretty speedy, haven't had an issue with them.
I'm already investigating what generation we have - but I'm almost certain our initial setup on at least one was using the admin !admin credentials, which means that it's documented _somewhere_.