(Disclosure: IBMer working in Power Systems, opinions my own)
For the BMC, it appears that they're looking to use OpenBMC, a project started by Facebook and now being continued by IBM.
They're also going to use the OpenPOWER firmware stack - Hostboot for system initialisation, Skiboot for runtime firmware/BIOS and the OCC firmware for on-chip thermal and power management. All of this is Apache-licensed.
POWER8 processors do require an external CPU to boot them - either an IBM Flexible Service Processor or a third-party BMC. This is the case with all current Power Architecture server chips, though not with Power embedded (Book 3E) chips. Booting a POWER8 chip is a bit more complex than comparable Intel CPUs in this regard, but as far as I'm aware it's primarily a design choice to put the initialisation complexity in firmware rather than hardware.
Can't comment about the other components of the system - I imagine it'd be fairly challenging to find a hard drive with open source firmware, but I wish them luck... FSF will still certify them as Respects Your Freedom nonetheless, I imagine. I'm still quite excited by this machine, as POWER8 is definitely the best choice for a high-performance libre system.