Pull back corn husks, leaving them attached at base of ear. Remove and discard silk; pull husks back over corn. Place ears in large bowl; cover with cold water. Let soak 10 minutes.
Meanwhile, cut off and discard top third of tomatoes. Using a paring knife, cut around wall of tomato to loosen flesh. Gently squeeze out seeds; discard. With a melon baller, scoop out tomato interiors, leaving the wall intact. Coarsely chop interiors; transfer to a large bowl.
Heat grill to high; lightly oil grates. Drain corn; arrange ears on grill. Cover and cook, turning occasionally with tongs, until husks are slightly charred and corn is tender, 15 to 20 minutes. Remove ears from grill. Holding bottom of hot ears with a towel, peel back husks and cut kernels off cob; transfer to bowl with tomatoes.
Add scallions, all but 2 tablespoons goat cheese, vinegar, and oil. Season with salt and pepper; toss to combine. Spoon filling into hollowed tomatoes; sprinkle with remaining goat cheese and, if desired, bacon.