Do Mac Pros use NUMA? 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.