1. In a small bowl, soak the dried mushrooms in the boiling water until softened, about 15 minutes. Remove the mushrooms and strain their liquid into a medium saucepan through a sieve lined with a paper towel. Rinse the mushrooms well to remove any remaining grit and chop them. Add the broth and clam juice to the mushroom-soaking liquid and bring to a simmer.
2. In a large pot, heat the oil and butter over moderately low heat. Add the onion and cook, stirring occasionally, until translucent, about 5 minutes. Add the garlic and rice and stir until the rice begins to turn opaque, about 2 minutes. Add the fresh mushrooms and cook for 1 minute. Add the wine and salt and cook, stirring, until the wine has been absorbed.
3. Stir in the dried mushrooms and 1/2 cup of the simmering stock; cook, stirring frequently, until the stock has been absorbed. The rice and the stock should bubble gently; adjust the heat as needed. Continue cooking the rice, adding the stock 1/2 cup at a time and allowing the rice to absorb the stock before adding the next 1/2 cup. Cook the rice until almost tender, about 25 minutes, and then add the shrimp and scallops. Cook, stirring, until the rice is tender and the shrimp and scallops are done, about 5 minutes longer. The stock should be thickened by the starch from the rice. You may not need to use all of the liquid.
Wine Recommendation: The full flavor of shrimp is reason enough to drink a full-bodied chardonnay with this dish. Try a bottle from California or Australia.