If you want get the RDMs defined in your vmware environment using PowerCLI, then you can just use this:
Get-VM | Get-HardDisk -DiskType "RawPhysical","RawVirtual" | Select Parent,Name,DiskType,ScsiCanonicalName,DeviceName | fl
(Remember to use the Connect-VIServer cmdlet before!)
Best regards,
Pablo
P.D: Got from this vmware's KB