Preheat a grill to medium high. Toss the tomatoes with 1 tablespoon olive oil, the garlic, 3/4 teaspoon salt and a few grinds of pepper on a large piece of foil. Add the thyme sprigs and bring up the edges of the foil slightly. Pour in the wine and fold the edges together to form a packet; set aside.
Brush both sides of the polenta rounds with the remaining 1 tablespoon olive oil; season with salt and pepper. Season the salmon with the chopped thyme, salt and pepper.
Oil the grill grates. Grill the foil packet until the tomatoes are soft, 10 to 12 minutes. Meanwhile, grill the polenta and the salmon skin-side down, 3 to 4 minutes; flip and grill until well marked and the salmon is just cooked through, 3 to 4 more minutes.
Divide the salmon and polenta among plates. Spoon the tomatoes and juices over the top. Sprinkle with the chives.