Short answer: No, we NEVER, under any circumstances, use a client's submitted file for another client's drumhead without the owner's express written permission.
Long answer: That said, we have had different clients submit very similar artwork in the past. With the ubiquity of certain types of images or designs and the ability of people to do all kinds of in-depth searches through Google Images and various microstock photo repositories, it is impossible for us to become "image police" for the thousands of images we receive every year. In these cases, our submitted artwork terms and conditions policy comes into play.
For example, we once received a nasty letter from a client who claimed that we used an element of their design in another client's drumhead. This was patently untrue -- the new client had submitted their own artwork -- and the the elements in question were two very common tattoo swallows (birds). A simple Google Images search returned literally hundreds of identical designs, and both clients likely sourced their elements from the same place. The point is that we can not be held accountable for the use of common and/or unoriginal elements in your or any other drumhead design.
In addition, images chosen from our image catalog are not exclusive and may be used by many different clients. However, the exact changes/additions/enhancements that you make in our CabCreator drumhead design tool are *yours* and will not be reproduced unless the client goes in and makes the changes themselves.
The bottom line is that we will NEVER reproduce your submitted artwork for someone without your express permission. So as long as your artwork is fairly original and includes elements that make it unique, your head will be the only one of its kind!