Very strange one this. It does list in the devices drop down of the google home app in HE, lets you select it, stays when you choose done and even appears on the 'In Use By' section of the device, BUT when you run the 'update devices' on google assistant it doesn't push across, and the selection in the google home app in HE becomes unselected and it is removed from the 'in use by' section on the device.
So I tried unlinking HE from google home and then re-linking and the device IS listed, but when you select it and complete the linking (enter password etc) it does not come across. And again is removed from the 'In Use By' section of the app.
It sure would be nice to ask google home the temperature of the hot tub! (yes very simple solution to float one of these in a sealed tupper ware container, but it works great!)