In a Dutch oven or soup kettle, saute celery and onion in oil until tender. Add remaining ingredients; bring to a boil over medium heat. Reduce heat; simmer for 25-30 minutes or until tender. Discard the bay leaf. Cool slightly.
Place the sweet potatoes, cabbage, and carrots into a slow cooker, then place the bratwurst slices on top of the vegetables. Sprinkle with the salt, thyme, rosemary, and pepper. Pour the wine and chicken broth over the vegetables.