When I worked for an MMO game company I constantly got dinged for OSX's ancient OpenGL support which limited what we could do (being cross platform). Now that I don't need it anymore they go way forward. Still it's great support. And add in the Borg Trash Can's dual video cards for lots of fun!
Funnily enough, only one of those two FirePros are connected up as a 'graphics chip'.
The intent of the Mac Pro, when you look at it, is to be a small, lightweight, ridiculously powerful OpenCL workstation. It has a single Xeon to handle systems tasks, two FirePros (one of which does graphics and computation, the other does only computation), and PCIe SSDs to keep the OpenCL cores fed and store their data.
