While it is certainly a good idea that a VPC has the same allowed VLAN list on all sides, it is not a requirement. Take a look at the output of "show vpc consistency-parameters global".
switch# show vpc consistency-parameters global
Legend:
Type 1 : vPC will be suspended in case of mismatch
Name Type Local Value Peer Value
------------- ---- ---------------------- -----------------------
QoS 2 ([], [3], [], [], [], ([], [3], [], [], [],
[]) [])
Network QoS (MTU) 2 (1538, 2240, 0, 0, 0, (1538, 2240, 0, 0, 0,
0) 0)
Network Qos (Pause) 2 (T, F, F, F, F, F) (T, F, F, F, F, F)
Input Queuing (Bandwidth) 2 (50, 50, 0, 0, 0, 0) (50, 50, 0, 0, 0, 0)
Input Queuing (Absolute 2 (F, F, F, F, F, F) (F, F, F, F, F, F)
Priority)
Output Queuing (Bandwidth) 2 (50, 50, 0, 0, 0, 0) (50, 50, 0, 0, 0, 0)
Output Queuing (Absolute 2 (F, F, F, F, F, F) (F, F, F, F, F, F)
Priority)
STP Mode 1 MST MST
STP Disabled 1 None None
STP MST Region Name 1 "" ""
STP MST Region Revision 1 0 0
STP MST Region Instance to 1
VLAN Mapping
STP Loopguard 1 Disabled Disabled
STP Bridge Assurance 1 Enabled Enabled
STP Port Type, Edge 1 Normal, Enabled, Normal, Enabled,
BPDUFilter, Edge BPDUGuard Disabled Disabled
STP MST Simulate PVST 1 Enabled Enabled
Allowed VLANs - 1,10,100-101,200-201 1,10,100-101,200-201,2
000
Local suspended VLANs - - -
Type 1 parameters absolutely MUST match, else the vPC will be suspended. "Allowed VLANs" is neither a Type 1 or Type 2 parameter.
You should be able to modify the allowed VLAN list without problems, but obviously try to keep things consistent regardless, otherwise you'll still have issues, even though the vPC doesn't get suspended.
EDIT: You probably already know this but just to be sure - include the peer-link in your VLAN changes, as the VLAN (not the entire vPC) will show up as "suspended" on all vPCs until you do.
Best Answer
First of all there is a big difference between VSS and VPC where Nexus vPC is introduced with Nexus 2,5 and 7K. The vPC is actually eliminate the need of STP on the member vPC ports and allow for efficient load sharing capabilities .The VSS on the other hand is a feature introduced with Cisco 6500 catalyst, its basically combines the Back plane throughput of the two systems which allows for high forwarding rate between ports, it also simplifies the management by making two physical switch operate as one logical Switch(like stack wise in 2960,3750 series). enter link description here
Second there is a difference between VSS and other redundancy protocoles like HSRP and VRRP , where VSS operate so far like Stack wise in 2960 and 3750 series single IP will manage all the chassis but in HSRP and VRRP you had to assign each chassis one IP and then gave them the Virtual IP but one drawback that VSS can't be supported in all chassis
Finally if you just want to obtain redundancy between chassis for fail over purposes you can run VSS,HSRP,VRRP for cisco IOS and VPC for Nexus. if you aim to also obtain single management IP you need to run VSS only but it is depend on the chassis