I'm wondering mainly because finding enough food for everyone is a concern, and you get attacked by a couple right at the start. I would think they are (since they are basically giant crustaceans), but you would probably need a knowledge (nature) check to remove the poisonous parts.
My players reminded me that food in the tropics spoils quite a bit faster, so unless they manage to keep the eurypterids alive in captivity they will probably only be able to eat them the first day.