Place 5-quart stock pot on stove. Add oil; heat over medium-high heat, until very hot. To make a dark brown roux, add flour and cook, whisking constantly, until dark brown but not burned, about 1 minute. Stir in onion, green pepper, garlic, salt, and thyme leaves; cook until onion and green pepper are tender, about 8 minutes, stirring occasionally.
Add tomatoes with liquid, okra, and water; heat to boiling. Reduce heat to low; cover and simmer about 30 minutes, until mixture thickens slightly.
Add shrimp, crab and hot pepper sauce; cook 10 minutes, stirring occasionally, until shrimp turn pink and opaque.
Ladle into soup bowls, add a generous spoonful of rice, and serve.