Heat oven to 450° F.
Toss together the potatoes, 1 tablespoon of the oil, and ¼ teaspoon each salt and pepper on a rimmed baking sheet. Roast, tossing once, until tender and golden brown, 15 to 20 minutes.
Meanwhile, combine the radicchio, olives, snap peas, chives, vinegar, 2 tablespoons of the oil, and ¼ teaspoon each salt and pepper in a large bowl.
Heat the remaining tablespoon of oil in a large nonstick skillet over medium-high heat. Season the scallops with ¼ teaspoon each salt and pepper. Cook until golden brown on one side, 3 to 4 minutes. Turn and cook until opaque throughout, 1 to 2 minutes more.
Toss the potatoes with the radicchio and serve alongside the scallops.