Its a tough one; there is no way to get a sugar free and vinegar free salad dressing, except if you did lemon and olive oil.
I have done the diet for 4 months while using italian and vinegerette dressing; it does set you back and is the worst thing you can have pretty much, but my body healed anyways. It will only extend the length of your treatment.
I found two dressings with apple cider vinegar; bragg’s makes one with no bad ingredients, and annie’s makes a raspberry vinegerette; the annie’s one also contains small amounts of sugar and other bad ingredients, but I can deal with it.
The ranch dressing contains dairy products which is definitely the worst of all ingredients for the diet; so you will have to continue on without it if possible.