I tend be really careful with Oyster Stout, but only because I'm a vegetarian and don't eat (or drink) fish.
I do know of one commercial Oyster Stout, made by Marston's in the UK that does not contain oysters, but was designed to be drunk with oysters. I come from London, and I grew up learning that a) you don't eat oysters unless they are still alive; b) you should always consume them with something fairly alcoholic to kill the nasties, and that c) the alcohol of choice is champagne if you're rich, and stout if you aren't. There are still some oyster places by the river in London where you can get oysters and stout, and I remember trips to the sea as a child where the adults slurped things from shells with potent black brews in hand.