In a large bowl, combine lemonade mix, Old Bay seasoning, and salt. Stir in oil to blend. Add shrimp and zucchini, and toss to coat. Cover and refrigerate until ready to grill, up to 8 hours. If using wooden skewers, soak them in water to prevent burning.
Thread shrimp, zucchini, and tomatoes on separate skewers. Grill zucchini, flipping occasionally, until tender, about 15 minutes. When zucchini have been on grill 7 to 8 minutes, add shrimp and tomato skewers, and grill, flipping once, until cooked, about 8 minutes.