You do not need an XBee dev board.
The socket on the 6UL Pro is UART 2.
Your Yocto build will need a library to talk to the module.
Personally, I prefer python but you can use whatever you prefer.
Then you just use the existing info in the library help which you can find on Github.
There is a GUI for setting the XBee, XCTU, but it does not come in a Linux ARM build.