>>> I'm assuming that by presenting the storage LUNs you mean adding a datastore
No, I'm talking about presenting the LUN from the storage system.
>>> Won't that process format the VMFS LUN and erase all the existing data?
Once you present a LUN to an ESXi host, which already contains a VMFS datastore (i.e. is formatted with VMware's VMFS file system), the host will detect the datastore, and there's no need to format it again.
André