Updated 2017: this note was written in 2015. Since that time, Xioami has expanded their home automation offerings significantly, and now have a number of devices using the ZHA 1.2 profile which many community members are using successfully with SmartThings. So if you buy something used on eBay, it may not work. If you buy something new, make sure it’s the one that is using the ZHA profile.
If they are the original xioami series they will not pair to SmartThings. They use their own proprietary encoding and can only work with their own controllers.
Smartthings uses the zigbee home automation 1.2 profile (ZHA 1.2). Can’t pair with other profiles or proprietary ones. Same issue as the original series Lowes iris devices, or the original series NYCE devices. Or control4 devices. They’re all using zigbee but they’re not using the same message encoding so they can’t talk to each other.
Whenever you buy something you want to use with SmartThings, and it’s Zigbee, check to see that it is certified for ZHA 1.2 or ZLL (which is the zigbee light LINK profile used by lightbulbs)
Other profiles like Zigbee pro, Zigbee green energy, zigbee medical, or individual company proprietary zigbee will not work.