I dont think that is the case and fractional reserve seems to be the name of the game for some of the ETFs. Would love some numbers regarding the long/shorts if you have them.
That certificate ensures the commodity is mine even if the holder gets bankrupt or some other disaster. Not having it there would be fraud, and my government does go around checking it.
I have a quite strong suspicion that this is universal. But well, I haven't checked this.