Cut off pointed end of garlic; place bulbs on a piece of aluminum foil, and drizzle with 1 tablespoon olive oil. Fold to seal.
Bake at 425° for 30 minutes; cool. Squeeze pulp from garlic cloves into a small saucepan. Set aside.
Cook tomatoes in boiling water for 30 seconds; drain. Peel, seed, and dice tomatoes; add to garlic. Stir in 1 1/2 cups olive oil, basil, 1/4 teaspoon sea salt and 1/4 teaspoon pepper. Set aside.
Sprinkle snapper cavities with remaining 1/2 teaspoon salt and 1/2 teaspoon pepper; insert rosemary sprigs. Brush skins lightly with remaining olive oil. Place fish in 2 lightly greased grill baskets.
Grill, covered with grill lid, over high heat (400° to 500°) 10 to 12 minutes on each side or until fish flakes with a fork.
Cook tomato sauce over low heat until warm. Spoon 1 cup sauce over fish Serve immediately with remaining sauce.