Light a grill. In a large bowl, toss the garlic and onion with the lime juice and let stand for 10 minutes.
Brush the corn with oil and grill over moderate heat until charred and just tender, about 10 minutes. Transfer to a work surface and cut the kernels off the cobs.
Whisk the mayonnaise and chile powder into the garlic, onion and lime juice. Add the cheese and corn to the bowl and toss. Season with salt, pepper and hot sauce.
Brush the scallops with vegetable oil and season with salt and pepper. Grill over high heat until nicely browned and barely cooked through, about 3 minutes per side. Spoon the corn salad onto 4 plates and top with the scallops. Serve with lime wedges.