According to their documentation, it uses the Thermostat device classes, so it should work in ST with the default thermostat device handler.
Since it only does heating, a lot of the tiles in the DH will be useless. This could be an easy project to learn coming up with your own DH if it works with the default (keep reading, someone’s already there perhaps). Note though that battery level reporting isn’t in that DH.
Also, since it’s battery operated, I would highly recommend performing the include process right next to the hub. Don’t be surprised if you have to try a few times, and that it’s found as a Thing at first.
Here’s someone (@meavydev) in your region that looks to have made an SRT321 work with ST, including the device handler you’ll need perhaps. I recommend getting included in this discussion:
Also, here’s documentation you need for your thermostat that may be handy to keep around: