This was resolved by cold booting the server. Warm boot didn't work. Once I did a complete shut down, it registered. Go figure. 
We just purchased a new blade system (DELL FX2). Each blade is configured with two fiber HBAs that are connected to two new downstream fiber switches. Each downstream switch has an ISL connection to a switch connected to the VNX. Each blade's HBAs  show up on the appropriate switch. Everything looks great. I zone the first blade, and all is well. All four paths show up in the 'initiator' screen in Unisphere. The host agent is checking in with the hostname. I can create a storage group and present LUNS. Terrific! I zone the second. Again, it's all good. Then I get to the third, and for some reason,  switch's 1's paths do NOT show up! Switch 0's paths are fine.  I double checked the zones. Deleted them. Re-added them. Disabled/Enabled the switch. I checked for the zones and aliases on the connected upstream switch. Everything looks great. I restarted the host agent, although I'm pretty sure the initiators should show up anyway. I can't understand why these aren't showing up Any idea of what I should try next?
VNX can't see initiators from one host, but only from one switch!