Melt the butter in a large Dutch oven over medium heat. Whisk in the flour and cook until toasted and browned, about 8 minutes, whisking constantly; the texture and color will be like a thin, amber gravy. Whisk in the cayenne until combined.
Add the onions and cook until tender, about 5 minutes, stirring frequently. Add the garlic and jalapeno and cook until tender, about 2 minutes, stirring constantly. Season with salt and pepper. Stir in the seafood seasoning spice blend, corn, okra and chicken broth. Bring to a boil, reduce to a simmer and cook until the gumbo has reduced slightly and is thickened, 20 to 25 minutes, stirring occasionally.
Meanwhile, combine the rice and 3 cups water in a medium saucepan. Bring to a boil and then immediately cover with a tight-fitting lid. Reduce the heat to low and cook until the rice is just tender and all of the water is absorbed, 12 to 15 minutes. Turn off the heat and allow to steam for 5 minutes. Fluff with a fork and cover with the lid to keep warm.
When the gumbo has reduced slightly and is thickened, stir in the crawfish tails and shrimp and cook until the shrimp is opaque and the crawfish is warmed through, 3 to 5 minutes.