No code is required. This is a primary-secondary controller network where the 2GIG acts as a secondary controller.
All devices would be learned into the primary, then the secondary linked. Compatible Z-wave devices would be shared with 2GIG.
This post goes over the basic process of adding a 2GIG panel as a secondary controller.
You cannot control the 2GIG Panel from a Z-wave controller (as in you cannot arm/disarm directly, etc.) Integrating allows multiple control methods of the same devices.