Put rice in a strainer and rinse thoroughly with cold, running water. Transfer to a medium saucepan, add 2 cups broth and bring to a boil over high heat. Turn heat as low as possible, cover rice and cook until tender, about 18 minutes; fluff with a fork.
While rice cooks, stir together cumin, thyme, gumbo filé powder, salt, pepper and cayenne in a cup. Melt 1 Tbsp. butter in a large skillet over medium-high heat, add seasonings and then shrimp, and cook, stirring, until firm, about 5 minutes. Transfer shrimp to a plate.
Add remaining butter to pan along with sausage, onion and garlic. Cook over medium heat, stirring, for 2 minutes. Add bell pepper and cook for 2 minutes more. Pour in tomato sauce and remaining 1 cup broth and simmer until vegetables are tender, about 5 minutes. Return shrimp to pan and cook, stirring, until heated through, about 3 minutes. Combine rice and scallion with shrimp mixture; toss.