The ISIS Source IP address should be configured whether or not the mgmt CLIP is in GRT or a VRF.
Basically, before 8.2, the ISIS Source IP and the CLIP GRT management were the same.
But from 8.2 onward they can no longer be the same.
As I said before, the ISIS Source IP in itself is not hugely useful and 8.2 will now quite happily let you run IP Shortcuts and L3VSNs even if you did not set one (this was not the case before 8.2). But if you run SPB with “spbm ip enable” and you did not set a ISIS Source IP the VSP will complain with warning messages in the log file.
The Admin Guide states:
You must configure a new loopback interface isis ip-source address if you migrate the
current ISIS IP address to the CLIP Management Instance when the IP address is the same as a
previously configured IP shortcut.
The other point raised by Peter, is that the mgmt vlan can only be reached from that VLAN. The intention of mgmt vlan is to manage a VSP which is acting as L2 only. If you create a mgmt vlan on a VSP which is acting as a L3 IP router, then you will observe that the mgmt vlan IP cannot be reached from other IP subnets.
The Admin Guide does mention this:
Packets sent to the VLAN Management Instance IP address must ingress the switch from a VLAN
port (or contain the VLAN ID) associated with the VLAN Management Instance. The system does
not route packets between the VOSS routing VLAN and the VLAN Management Instance.
So, if your VSP is doing L3, use mgmt clip
Whereas if your VSP is doing only L2, use mgmt VLAN