Quick post: If you buy the DroboElite because it’s on the VMware vSphere HCL and want to use VMware Data Recovery don’t add the space as an RDM.
The Drobo is not compatible with the format scheme of the DR appliance and you’ll toast your Drobo. Trust me. If you have data on the Drobo you need, their tech support will need to write a custom firmware version wiping out the RDM.
Instead, create a VMFS datastore and add a VMDK for VDR.