Mix buttermilk, oats, butter, eggs, brown sugar, baking powder, baking soda, syrup, cinnamon, salt, and nutmeg together in a large bowl; fold in raisins.
Oil a griddle over medium heat. Drop batter by large spoonfuls onto the griddle; cook until bubbles form and the edges are dry, about 5 minutes. Flip pancakes and cook until browned on the other side, 2 to 3 more minutes. Repeat with remaining batter.