It won't cause them to conflict in the network space but you wouldn't be able to attach to both of them from a VM if they used the same secret UUID.  On the other hand our puppet currently can't set up that configuration right now either (for other reasons than just this one).  We certainly could make that possible by changing things around but at the moment I believe we set up Cinder+RBD by supplying it precisely one key in as class's arguments, so there are reasons other than this one that would stop us making use of it.

If we changed it around we would presumably move from a class to a define, and we could pass in a UUID with each key.  It's still greatly simpler if that UUID comes from the puppetmaster, though, since it has to go to both virsh and Cinder.