1. Preheat grill to medium-high heat.
2. Place a grill basket on grill.
3. Place potatoes and 2 teaspoons salt in a saucepan; cover with water. Bring to a boil; cook 2 minutes. Remove from heat. Let potatoes stand in hot water 5 minutes. Drain; cut into 1/4-inch cubes.
4. Melt 1 tablespoon butter; brush evenly over corn. Place corn on grill rack coated with cooking spray. Place potatoes in grill basket coated with cooking spray. Grill corn and potatoes 15 minutes or until slightly charred, turning occasionally. Cool corn slightly; cut kernels from cobs. Place 1 cup corn kernels in a food processor; process until smooth.
5. Melt remaining 2 tablespoons butter in a medium saucepan over medium-high heat. Add onion; sauté 3 minutes, stirring occasionally. Add remaining 1 teaspoon salt and red pepper; cook for 30 seconds, stirring frequently. Stir in potatoes, remaining corn kernels, pureed corn, milk, half-and-half, and thyme sprigs; bring to a simmer. Reduce heat; simmer 20 minutes, stirring occasionally. Discard thyme sprigs. Stir in chives and remaining ingredients.