Some of this is heavy opinion and some is experience. First, 10.7 was a terrible OS for Xsan support. Some of the issues you may be experiencing may be due to 10.7. I for one, avoided it like the plague.
Next, the issues you are describing sound like they could be DNS related or possibly related to how you defined your zones and your ports (target vs initiator). The place to look is your system log on these units. You should be seeing SCSI initialization errors from the FC cards. You may have loop arbitration issues or something else related to the way the FC ports are configured.
Any reason why 10.7.x was selected?
If "sudo cvlabel -c" hangs when listing LUNs, xsanmgrd (or servermgrd in 10.7.5) will also hang when it checks LUNs on behalf of Xsan Admin. This might cause Xsan Admin to think that authentication has failed.