Sprinkle shrimp with salt. Warm olive oil in a large skillet over medium-high heat. Add shrimp and sauté, stirring, until pink and cooked through, 2 to 3 minutes. In last minute of cooking, add garlic and red pepper and continue to sauté. Remove shrimp from skillet and set aside.
Add tomatoes and juice to skillet and bring to a boil. Lower heat and simmer until tomatoes are soft and sauce has thickened, about 10 minutes.
While tomatoes are cooking, bring 2 cups water, vegetable broth and 1/2 tsp. salt to a boil in a medium-size saucepan. Slowly whisk in polenta. Reduce heat to low and cook until polenta is thick and smooth, stirring often, about 5 minutes. Stir in butter and Parmesan.
Put polenta into bowls, spoon tomato sauce over polenta and top with shrimp.