Preheat oven to 425°F.
Place grapes on a rimmed baking sheet. Drizzle 1 tablespoon oil over the grapes and toss to coat. Roast until the grapes start to burst, about 10 minutes. Let cool for 5 to 10 minutes.
Meanwhile, combine vinegar, honey, mustard, herbs, salt and pepper in a large bowl. Slowly whisk in the remaining 2 tablespoons oil.
Add radicchio, arugula and the grapes to the bowl and toss to coat. Top with goat cheese, pine nuts and pomegranate arils, if desired.