billmathews,
What server model are the ESXi 5.1 running on ? OME only supports WSMAN for discovery of ESXi hosts and other protocols are not supported. However if other protocols other than WSMAN are enabled in discovery wizard, they should be ignored.
OME does not supporting excluding hosts per discovery range. I'll forward that as a feature request to the Dev. team.
Thanks,
Raj Shresta