Bring milk and 1 1/2 cups water to a boil in a large saucepan over medium-high heat; gradually whisk in grits. Reduce heat to medium-low, and simmer, stirring occasionally, 10 minutes or until thickened.
Meanwhile, sprinkle Creole seasoning over shrimp. Sauté garlic in hot oil in a large skillet over medium-high heat 30 seconds. Add shrimp, and sauté 3 minutes or until shrimp are almost pink. Add green onions and next 3 ingredients, and sauté 3 minutes.
Stir potatoes and next 4 ingredients into grits. Serve shrimp mixture over sweet potato grits.