Full carbon bike with Zertz insert? I wouldn't chance it if it was my bike. I got a CR1 carbon frame bike and I can feel some flex when I hit bumps. I'm no expert but I think having anything clamped to a carbon Seat stay is not to good of an idea if there will be some flex on your frame. Beside that, you may need to use p-clips which also be stress on the seat stay when you tighten those around the carbon along with the weight of the load and the rack.

What are you trying to carry? Small item can be fitted in extra pack such as a frame pack on the triangle of the frame. If you need more, than perhaps a Topeak Dyna Pack which clamps on to the seat post will be ok. Just beware of the torque needed to tighten the clamp around the carbon post. If you are carrying books and such, I would go with a messenger bag or backpack. In another thread, someone suggested an Old Man Mountain rack for my FS MTB. I've never tried the product myself but it might work. It used the skewer as part of the rack mounting. Something like that may be better than clamping to the seat stay since most of the load will be on the wheel instead of the seat stay, I think........