Also, the following thread had some discussion from SmartThings staff about which smartthings branded devices sold in the US might work with the UK hub:
This is as of the most recent generation of devices.
Amplified devices:
US Hub
US Outlet
US Water Leak
UK Hub
Unamplified devices:
US Presence
UK Presence
US Motion
UK Motion
US Multi
UK Multi
UK Outlet
UK Water Leak
And a note from our engineer:
But the presence of an amplifier doesn’t necessarily mean that the signal is being transmitted at a higher strength. In the UK hub, for example, the amplifier helps with the RX side of the transmissions, but the TX stays within the lower UK limit.