I am confused, how exactly do you expect to share a RDM across serveral Guest. the locking mechanism will prevent the 2nd and subsequent VMs from using it.
think if this from the perspective of a physical machine. you are asking multiple guests to share the exact same hard drive.
Each VM will require their own LUN unless you are attempting to create a MSCS cluster.
If you want to have vMotion then you will need to create a virtual RDM connections but you will be limited to 2TB disk size