Natter, if the sugar is from a natural source and not added in (just the sugar from the tomatoes or from the fruit) it should be fine. It's the added sugar that you need to worry about. Hence, the majority of dressing doesn't have any natural sugar...all of it is added in, so you don't want more than 3 grams. In things that don't have added sugar, like V-8, I think the amount of sugar is fine. However, in the Progresso, there is probably added sugar and the sugar from the tomatoes, so you want something like Hunts that only has tomato sugar, not added sugar.
Wow, that hurts my head to read!
Does it make any sense?