If you’re referring to the Xiaomi Mi-home sensors, search the forums here for “xiaomi”. The majority of these sensors do work with SmartThings, but they don’t use a standard zigbee protocol, so some of the functions aren’t able to be fully exposed or utilized. They also can be finicky to get paired, and some people have had issues keeping them connected to their network. There are some repeaters that kick them off the network because their check in period is just longer than the repeater requires. I have over a dozen Xiaomi devices which have been working great for me for over a year. You’ll need to use custom dth’s for all of them.
The newest Xiaomi sensors are using zigbee 3.0, which means integration with SmartThings should be easier and more reliable. The vast majority you find for sale right now however are the older non standard zigbee protocol.
You can use these with the Xiaomi gateway, but integration between the Mi Home gateway and SmartThings will likely be limited. And currently only the China server supports the zigbee devices and gateway, so when you set up the Mi Home app, make sure to set your location as China.
And typically these sensors can be find much cheaper on sites like Gearbest, AliExpress, and Banggood. All of my Xiaomi sensors came from Gearbest.
Here’s where I’d start reading: