When using MCT the cluster rbridge-id must be unique on each device.
With respect to VRRP(e) VRID as you mention the same VRID can be used in each instance running in their own VLAN.
I have seen this done both ways many times, some just set VRID as 1 in every VLAN which is valid and works fine. Others vary the VRID for each VLAN but obviously there is only 1 to 255 available.
It simply comes down to what works best for you there is not a hard and fast rule for this.