I brewed the BYO Black Pearl Oyster Stout, this seems like a perfectly normal ingredient. My brother in law does a Feast of Seven Fishes every Christmas, he jokingly asked for a beer with seafood in it, he'll either be stoked or horrified.
There's a nano brewery in Asheville (located in a seafood restaurant) that brews an oyster stout - I always just assumed they used just the shells as a calcium addition to the water. Maybe they add actual oysters too? Curious to see how this turns out.