Apologies, should have included that fact in the intial post. The vmkfstools command requires the --vihost option when --server references a vCenter. Here is the error message I get when trying to leave --vihost off:
The --vihost option must be specified when connecting to vCenter.
For a summary of command usage, type '/usr/bin/vmkfstools --help'.
For documentation, type 'perldoc /usr/bin/vmkfstools'.
Thanks for the suggestion!