When you use physical RDM mapping, SMART data is beeing passed -through. The virtual scsi controller that is presented to the VM is the problem. DSM doesn't have the right driver for it, hence it cannot read the SMART data. You can try installing vmtools in DSM and see if there is a change. If not, somebody must write a driver for vmware paravirt/ lsi sas/parallel for DSM.
You can always passthrough the whole controller to the VM with intel vt-d for DSM direct access to the controller.