I just added a few LUN's to our new EMC VNX, and the LUN ID's are not consistent..
Screenshot from EMC Unisphere
Screenshot from VMWare vSphere
If you study the two screenshots carefully, you'll notice that the Unique ID is identical, yet the LUN ID's differ. I'm a bit at a halt here, and I'm not sure if I should call EMC and blame them, or start searching the net for potential vSphere bugs..