Is the Ethernet Pro a 3.3V Arduino? The schematic dated 3/31/2011 says the ATmega328p is powered by 5V. If I am right about the 5 volts, I expect the shield to work with that board. I think the Arduino Pro 328 3.3V/8MHz and other 3.3V Arduinos will not work without modifying the Wixel Shield. Let me know if you are interested in the details of the modification.
If you test any Arduinos that work with the shield that we don't have on our list, please share them with us!