Identical hardware is definitely a big plus when your guest has optimizations relating to NUMA, and your guest and application can take advantage of them. With vNUMA, the level of optimization and the benefits provided by it depends on the guest, as well as the hardware, so having identical NUMA architecture at the host level will provide the most benefits. The Performance guide (http://www.vmware.com/pdf/Perf_Best_Practices_vSphere5.1.pdf)
has additional details.
-KjB