When I'm cooking, I tend to work largely on instinct, rather than by referring to recipes, etc. Most of the time I'm pleased with the results of my instinctive actions but I do occasionally get it badly wrong.
Having written a disclaimer, I'll now state that my instinctive suggestion (if you simply want to counteract the sweetness of the sugar) is to add some black pepper. However, if you want to improve the flavour of the cabbage at the same time, try some Dijon mustard (or even a small amount of English mustard).
Chris