Hi, Thanks for your question. Are you using an internal vcenter or an external one? It needs to be separate from the cluster. [URL] and [URL] Let us know if you have any additional questions.
for localized management of a 2 node vxrail cluster, can the physical witness appliance host the vecenter server as well as operating as the witness appliance or is an additional appliance needed specifically for vcenter? Based on the diagram outlined in the planning guide it indicates that vcenter can operate on the same single witness appliance as long as it is separate from the 2 node vxrail cluster.  
VxRail 2 node cluster witness host | localized managment