Line a plate with parchment paper or wax paper; set aside. Combine buttermilk, salt, and black pepper in a shallow dish. Add pickles; set aside.

Place cornmeal, flour, seafood seasoning, and 1/4 teaspoon Cajun seasoning in a large, resealable plastic bag; shake to combine. Add pickles, a few at a time, and shake gently to evenly coat with cornmeal mixture. Remove pickles; place on the prepared plate.

Heat oil in a deep fryer or heavy deep skillet to 365 degrees F (180 degrees C).

Lower pickles carefully into the hot oil in batches. Fry until golden brown and slightly crisp on the outside with a moist interior, 1 to 2 minutes. Drain on paper towels. Repeat with remaining pickles.

Combine buttermilk ranch dressing and remaining 1/2 teaspoon Cajun seasoning in a small bowl. Serve as a dipping sauce for warm fried pickles.