That is NOT how you would normally do that.
You can have separate "control networks" (Control Network A and Control Network B), if your main server has been set this way,, those specific control networks would need to be "replicated" over to the ESS Site (the SAME LAN segment via a Layer 3 switch/dark fiber). For your S8500B ESS Server to be able to control the IPSI's at the main site, you would setup the SAME control networks at the ESS site, but just use different IP's for the IPSI's at the ESS site, and different IP's for the S8500B's ESS Control Network A and Control Network B. You would normally use a few ports that would be in each CN, they would normall y be in the VLAN for that control network.
You need the S8500B Dual NIC card to create separate Control Network A, and Control Network B at the ESS Site. You of course also need dark fiber and Layer 3 switches to be able to replicate those same LAN segments at both sites.
If you can't replicate the dedicated control networks between both sites, your only other choice is to use the "Corporate LAN", but of course there is no isolation then...
Mitch
AVAYA Certified Specialist