You have migrated VM's with a vRDM they are completely different beasts, the creation of a pRDM will create a direct link between guest and the HBA of the Host it is sitting on, this is effectively the same as attaching a com port or a CD/DVD from the Host directly to the Guest.
These acts raise a red flag with vMotion and will prevent the migration.
I am still struggling to actually understand what you are trying to do with this single RDM to multiple guests scenario. for what purpose are you trying to do this.
