Having trouble pairing these two Xiaomi devices

Only the “Xiaomi Smart Wireless Switch” you linked to is a ZigBee device. It’s also known as the “original” Xiaomi Button, and you can find my updated device handler to help it to work with a SmartThings v2 or v3 hub here:

The Yeelight Smart Dimmer switch, however, is a Bluetooth device, or at least the description in your link claims as such.

The only way to get a Bluetooth device working with SmartThings is to use some kind of “bridge” solution between the manufacturer’s proprietary interface and the SmartThings hub. There is a solution that allows linking a Xiaomi Gateway hub with SmartThings, but it doesn’t list support for the Yeelight Smart Dimmer switch, so I would recommend asking the author about it here:

Good luck!!