So here they are:
http://www.xlnaudio.com/products/kitpiecepak

Does anybody know if they are unique or not. Are they contained within other ADPaks? Is there a list if they are?

Googling doesn't seem to come up with anything..

Thx.

The kit pieces are unique, and can be added to existing kits or used in place of an existing piece in a kit. I have the Ludwig snare, and a couple of the bass drums, but I really like having all of the "world" kit pieces for use in the Flexi 1-3 slots.

They are unique. 
 
I am not sure when you acquired your AD's, but I think a little while back, they did come with 1 bonus Kitpiece, which was the Pearl Masterworks Piccolo Snare.
 
Just open your AD drums and check by looking in your kitpiece selection drop down (if you have the AD installed already of course).
 

They are unique and non redundant ....  chosse them to complemente what you have and answer your need ;)