Gotcha, we have had users report some success using the Harmony Remote in the past with the Z-wave Home Extender. This post has a description of adding it to their panel and using the remote.
Largely the remote is used in parallel to your panel and Alarm.com. Secondary Z-wave controllers are not managed through Alarm.com and your chosen service plan through Surety would have no effect on usage of a third party device. It would just come down to compatibility between versions and if the controllers play nice.