When you double tap a specific homeseer switch, it sends a central scene command to the SmartThings hub, and that then gets processed by a smart app which tells the hub to send the appropriate messages to whatever devices are in the group. This is one of the advantages of using SmartThings. The other devices could be any other Z wave device, it could be a zigbee device, it could be a Wi-Fi device. As long as SmartThings can talk to it, it can be in the group. So in that sense, the other devices can be pretty much anything you want which has a radio to talk to SmartThings and can receive a command.
That does leave out some things. The GE auxiliary switches, for example, don’t have a radio at all – – they are designed only to work with a GE master switch and communicate by physical traveler wires to that master.
But other master switches of any protocol that are controllable by smart things could be included in the group.