It depends on how the manufacturer of the device implemented standards, and/or if propriety stuff was done. A perfect example would be the Lowes first gen Zigbee devices. They technically were Zigbee, but they used a profile that only their hub could use. The gen 2 devices are a different story, and those work with ST. Z-Wave isn’t any different with examples like this.
The device you’re looking to order (TZ71 pictured) does not work with the US hubs because of it’s frequency of 868.42 MHz. At least from what I could tell from the link. Looks like they reference 5 or 6 devices in that link you provided.
All that said, if the device did use standards and the manufacturer documented what was used, then yes you could build a device type if ST didn’t have one. A good example would be the Philio line of devices, and even the new Aeon doorbell. Even a wifi device that has an API available can be integrated - a good example is the Thinking Cleaner wifi module for a Roomba. Given enough time and testing, you could technically make almost any device work.