I agree with Jacob, the ISC
VLAN cannot be enabled for ipforwarding. However you could have a L3 vlan using the ISC
PORTS.
That being said, I'm not sure to understand what you want to do. With MLAG, you can run VRRP in Master/Backup typical state, or use Fabric Routing to act in Master/Master. Losing the ISC connection is always a bad thing, that's why we recommend to have a LAG.