Does Mac OS X make use of NUMA on Mac Pros with two (or more) CPUs?
This is a partial answer
The processors in the current mac pros use Xeon processors e5620 and x5670s with Intel's QuickPath Interconnect
QPI is Intel's implementation of NUMA and takes place fully within the processor just as HyperTransport is AMDs
I would have to admit in not being sure if that takes OSX out of the equation entirely or even mostly. Modern processor architecture has improved since the original NUMA concept that the original requirement for software support is probably,now, immaterial.
No Mac Pro supports NUMA, their memory are configured in interleave mode.
Highly memory intensive application faced with incorrectly allocated (cross NUMA node) memory pages can still cause significant (>20%) performance issue albeit "modern processor architecture" (I'm an HPC admin a regularly benchmark / troubleshoot system performance issue).
And someone else has installed a NUMA aware OS (reads: Linux) onto a Mac Pro and finds only a single NUMA node, which shows that the firmware configures the memory to run in interleave mode (non-NUMA configuration). While this is slower than a properly configured NUMA system, it is still faster than an incorrectly configured / allocated NUMA system.
With this, we may reason that the mach/xnu kernel is likely non-NUMA aware.