Zigbee specification allows for many different “profiles“ and they do not all work together. It even allows for custom profiles.
Smartthings supports part (but not all) of the Zigbee 3.0 profile.
Zigboat is NOT certified for Zigbee 3.0. In fact, because it describes tunneling, I’m pretty sure it’s using a manufacturer proprietary profile, and will only work with its own gateway.
There are lots of certified zigbee devices that don’t work with smartthings, so you have to research a little deeper to find out the profile. For example, control4 Zigbee devices generally don’t work with SmartThings. Neither do green energy Zigbee devices like the friends of Hue switches.
FAQ: Zigbee Application Profiles, or why not all zigbee devices work with SmartThings