Yep, separate Genius Hub and SmartThings networks. They only communicate through the api - there’s no fundamental change to the operation of the Genius Hub at all. It’s through the remote api (hub-server-1.heatgenius.co.uk), not on LAN, partially because I couldn’t initially figure out how to make LAN requests which worked, and then, once I did, because I couldn’t figure out how to pass the necessary information to the callback.
- Pull down the smart app (Genius Hub Integration) and the three device handlers (Genius Hub House, Room & Switch) into SmartThings.
- Install the smart app - give it your Genius Hub credentials.
- Go back into the smart app after installing, and select which devices you want to be able to control. This will create child devices using the device handlers. (I didn’t really want them all, so it doesn’t set them all up automatically.)
The Room device shows the current operating mode (footprint, timer, override, off), current temperature, min battery of the various devices in the room. You can set the override temperature with the up/down arrows - this overrides for 1 hour. In override mode there’s a button to press to increase the override period by a further hour.
The House device works a bit differently to set an override temperature, given that it’s overriding many rooms rather than a single device. You set the target temperature with the up/down arrows, and then hit the override button to activate the override. It does override all rooms in the Genius Hub, regardless of whether they’re imported into SmartThings.
The Switch has two modes, which you can choose between in the device settings. In the default Genius mode, it’s pretty similar to the room - turning on/off applies an override for an hour, and you can increase the length by additional hours. In Switch mode, it operates like any other switch in SmartThings - permanent on/off state. This applies the override periodically in Genius Hub.
The state is refreshed from the Genius Hub api every 5 minutes, so if you make changes in the Genius Hub app they’ll show up shortly in SmartThings.
I’ve not yet looked into how well any of the devices work under other smart apps or webCoRE, though I’ve tried to use appropriate capabilities and additional actions and attributes, so my hope is that they will without too much tweaking 
Any feedback on things which don’t work, or which could be better, appreciated. I know there’s such a thing as linked rooms - which won’t necessarily work as I don’t currently have any, but that’s on the to do list. As is a way of not just defaulting to an hour for the override.