I am not seeing a related Surety subscription. In general, if you are able to see or control the z-wave devices in the website, you would have the same function in the app.
I cannot confirm how the 2GIG GC3 handles the ZRTSI or if it is compatible.
Are you seeing the devices under the manage devices page in Alarm.com or on the lights page? If you do not see a lights page, it is possible your plan does not support those.
Your dealer would need to adjust your plan to allow z-wave device control if that is the issue. Please reach out to your dealer for info.