Broadly speaking Pro Tools seems to be moving towards a more open situation but it apparently won't talk to some of the earliest Mboxes. It certainly works OK with both my Eleven Rack and Mbox Pro 3rd Gen and (because it uses an ilok key for authorisation not the presence of the hardware) it will run without anything connected if you (for instance) just want to do some editing work.
Whether it works with any given non-Avid hardware is probably still at the 'suck it and see' situation, but here's another quote:
From the What's New pdf:
"Support for Core Audio hardware (including Mac built-in audio) with supported Core Audio drivers installed.
Support for ASIO hardware with supported ASIO drivers installed"