It's interesting since AMD doesn't supports their hardware on FreeBSD AFAIK, so they're probably rolling some custom drivers too.
Yep, thats right, though interestingly since we have had no help in the form of binary drivers from AMD, the open-source radeon driver is actually pretty usable for 3D (almost on par with that in Linux). However, since Nvidia provides binary blobs for its hardware, the open-source "nv" is utter shite (nowhere near the usefulness of Linux's Nouveau).
Moral of the story, AMD has had to be cruel to be kind ;)
All I know is that if I was that skilled developer putting all that effort into developing a highly complex driver, it must be soul destroying to know that in ~5 years when the new console comes along, all your effort will be completely lost. I bet they would love to open-source their work and prove to the world that they are one of the rare breed of programmers, smart enough to be able to create something like that!
Edit: Thinking about it. I bet all AMD did was release the specs for their hardware to Sony and they did it all in house. Afterall, AMD's UNIX drivers are extremely low quality (no 2D acceleration for a start) which would be an issue for the PS4.