Place sweet potato and 1/4 cup water in a 1 1/2-quart microwave-safe bowl. Cover and microwave at HIGH 5 minutes or until tender. Mash 1/2 of sweet potato with a fork. Reserve remaining 1/2 of sweet potato and cooking liquid.
Combine broth, remaining 2 cups water, and reserved cooking liquid in a 3-quart saucepan. Bring to a simmer (do not boil). Keep warm over low heat.
Heat oil in a 4-quart saucepan over medium heat. Add shallots; sauté 3 minutes or until tender. Add rice; cook 2 minutes, stirring constantly. Stir in wine; cook 2 minutes or until liquid is nearly absorbed, stirring constantly. Add broth mixture, 1/2 cup at a time, stirring constantly until each portion of broth is absorbed before adding the next (about 27 minutes total). Stir in mashed sweet potato, reserved diced sweet potato, and corn; cook 2 minutes, stirring constantly. Remove from heat. Stir in cheeses and remaining ingredients.