Heat grill to medium (350°F to 450°F). Pat crabs dry. Brush lightly with 2 tablespoons of the oil, and sprinkle with salt and pepper. Grill, uncovered, until crabs are browned on one side, about 5 minutes. Turn crabs, brush lightly with remaining 2 tablespoons oil, and grill until browned, about 5 minutes. Transfer crabs to a plate, and serve immediately with lime wedges and Roasted Tomato Salsa.