If you wanted to communicate between your test network vlan and the other vlans then yes, you would have to create a port channel subinterface similar to the others on the core switch. Once you have configured the vlan on the necessary switches, console to your core switches and create a new subinterface as follows:
(config)interface port-channel 1.x (where x is the new vlan number)
(config-subif)encapsulation isl/dot1q x (using either isl or dot1q encapsultion. All subinterfaces within the port-channel must use the same encapsulation so look at what the others are set to. The x value should represent the vlan number of your test network)
(config-subif)ip address x.x.x.x x.x.x.x (This should be equal to the ip address of the default gateway configured on the workstations within the vlan. This will provide intervlan routing of IP packets!)
Don't worry about the admin group. As far as I'm aware it is only used to show a specific channel when multiple channels exist on a switch. For example, if you have 10 channels configured and only want to see information regarding one of the channels, on a switch you would enter:
show channel group x (where x is the admin group number). You can set the admin group to a value yourself (rather than it being automatically assigned) but spanning tree then has to reconverge leaving users offline for approx 30 seconds.
Hope this helps, let me know how you go on!
