You can use the shield from Arduino, but only in the "Micro" mode (the little switch on the shield) makes sense for the Galileo. Communication from the XBee won't be sent via USB as on the regular Arduino as describes on the shield page.
If you want to communicate with the XBee from the computer, you can upload a simple sketch that hooks up the two serial ports (the one on the Galileo that is connected to pin 0 and pin 1 which is the XBee and the one going to the computer)
In the Arduino environment these two serial ports are called:
- Serial (the one that communicates with your computer)
- Serial1 (The one that is connected to the XBee)