Hi Bob,
The schematic and other design files for the Arduino version of the CN0216 can be found in this zip file (http://www.analog.com/CN0216-Shield-DesignSupport )
There is actually a whole wiki page dedicated to the CN0216 Arduino Shield (CN0216 Shield Evaluation Board User Guide [Analog Devices Wiki] ) but because there is no hardware ordering capability on the wiki, we needed to add the ordering information to the CN0216 web page.
Without looking at the designs, my guess is that the ADG3308 is only present on the SDP version of the board because of the 3.3V requirements coming from the SDP. I believe you won't find this on the Arduino version, and like you said should work with 5V with no problem.
Brandon