A guide to adding Z-wave devices on the 2GIG Panel can be found here:
Whether you initiate the process on the panel or within the Alarm.com app, you are placing the panel in Z-wave inclusion mode and then triggering the device’s learning procedure to pair it with the panel. There is no difference in how the panel will report the device to Alarm.com whether the process is started on the panel or the app.
Generally I like to recommend following the steps on the panel screen for that reason.
There can be a delay in the panel reporting new devices to Alarm.com. This is pretty common on the 2GIG GC2.
If you notice the new Z-wave devices are not found in Alarm.com you can visit the system manager here and use the Send Z-wave Device List to ADC option to sync your panel devices with your account. This option sends a dealer level request to the panel to check the equipment list.