Combine scallops and snapper in the bowl of a food processor; pulse until combined. Combine potato, dill, and next 5 ingredients in a large bowl; mash well with a potato masher or large fork. Stir in scallop mixture, chorizo, and crabmeat; stir well to combine.
Place cornstarch, eggs, and panko in 3 separate shallow containers. Divide croquette mixture into 18 equal portions; form portions into balls. Roll each ball in cornstarch, then eggs, then panko. Set aside on a plate.
Heat oil in a large pot to 330°. Carefully fry croquettes, in batches, 3 to 5 minutes or until golden brown. Remove croquettes from oil using a slotted spoon; place on a paper towel-lined platter. Immediately sprinkle croquettes with kosher salt and black pepper as they are removed from oil. Serve with Rum Aïoli and pepper sauce, if desired.