I can’t speak anything else, but as far as the above…
- it has always been possible to add another nonST Z wave controller as a secondary, it just didn’t work very well. But that’s exactly how people are using the Aeotec USB stick or the Homeseer zstick when they want to use the zwave utilities that come with those controllers on their ST network. They add it as a secondary. There are also people who have added some other Z wave controllers as secondary’s for other reasons, such as the Staples connect integration.
FAQ: Is there a way to see the Zwave mesh network map?
But you couldn’t add a smartthings hub as a secondary to another smartthings hub as a primary because the cloud account would get confused.
- Setting everything in number one aside. The SmartThings models which have “sub hubs” did receive firmware changes a few months ago so that now the sub hubs will all work as Zwave repeaters and zigbee repeaters for the primary hub. It’s not clear to me whether they show up as a secondary controller or just as a “thing“ which happens to be a repeater, but that part of what the customer service agent was saying is true. When the issue is that you need a repeater in another part of the house, you can improve both the Wi-Fi mesh and the zwave mesh at the same time with one of the sub hubs.