Does the EdgeADC support Gateway mode?

Yes, the EdgeADC supports Gateway mode, and you can set this using the Connectivity option in the Advanced tab of the Real Servers section.

Gateway mode allows you to route all traffic through the ADC, allowing the Real Servers to be routed via the ADC to other networks via the ADC virtual services or hardware interfaces. Using the device as a gateway device for Real Servers is ideal when running in multi-interface mode.
Load balancing persistence policies are also restricted to Least Connections, Shared IP List Based, Round Robin and IP List Based.

This method requires that the Real Server sets its default gateway to the ADC’s local interface address (eth0, eth1, etc.). Please refer to the Real Server Changes section in the Administration Guide.

Please note that Gateway mode does not support failover in a cluster environment.