Turn the broiler to high and arrange a rack 4 inches below broiler. Line a baking sheet with foil.
Lightly spray the corn with cooking spray, then place on the baking sheet and broil until soft and beginning to char. Remove from the oven and let cool completely.
In the meantime, prepare the blackening seasoning. Add the paprika, cayenne, onion powder, garlic powder, thyme, oregano, 1 teaspoon salt, and 1 teaspoon pepper to a bowl. Whisk to combine the seasonings.
Spoon 1 tablespoon of seasoning mix over each filet and rub, using your fingers, until completely coated. Flip the filets and repeat on the other side, coating the entire filet.
Brush the tops of the catfish with butter.
Heat a cast iron skillet or griddle over medium high heat. Spray the pan lightly with oil. Once the pan is beginning to smoke (but not smoking rapidly), add the catfish, buttered-side down. Cook for about 2 minutes, or until catfish has blackened.
Brush butter on the top side and flip, cooking until blackened, about 2 minutes. Remove from the skillet.
To make the salsa, slice the corn kernels away from the cob and place in a bowl. Mix with tomatoes, onion, basil, lime juice, and olive oil. Sprinkle in 1 teaspoon each of salt and pepper, adding more as needed to taste.
Serve the blackened catfish with the corn salsa. To tame heat, serve with lime wedges.