I'm not really up-to-date with SmartThings, but I did take a look at the install instructions for the addon. It appears that it uses the AD2PI with an Arduino rather than the Raspberry Pi. I assume it's because the SmartThings shield is necessary. It may be possible to get the AD2USB to work with it since it's just a USB-to-serial device, but I'm not familiar enough with Arduino and it's USB support to say one way or the other.
The guy behind that project has some good build documentation you can find here:
https://github.com/d8adrvn/AD2SmartThingsI'm sure we can arrange a return (minus shipping) if you want to pick up an AD2PI instead. Just email
ad2usb@support.nutech.com and reference this thread and we'll get you taken care of.
Thanks!