personly i would upgrade on the usb disk instead of creating a new one.
but you should be fine to add the datastore and find the vm's and add them back to the inventory
2 things come to mind at the moment
datastore VMFS version (upgrade to 5.x) planning to upgrade?
and more important the networking have to be correct.
with regards
kind regards
Vervoort Jurgen
VCP6-DCV, VCP-cloud
http://www.vdssystems.be