In a medium saucepan, stir together tomatoes, sugar, garlic, mustard, and 1/2 cup water; season with salt and pepper. Bring to a boil; add pork, and simmer, covered, until tender, 18 to 20 minutes. Transfer pork to a plate to cool. Simmer sauce over medium, uncovered, until reduced by half, about 20 minutes.
Meanwhile, make slaw: In a bowl, whisk together mayonnaise, 1 tablespoon vinegar, celery seed, and 1 tablespoon water; season with salt and pepper. Add cabbage, and toss to coat.
Shred pork with 2 forks, and return to sauce; stir in 1 teaspoon vinegar. Serve pork on rolls, topped with slaw.