Atkins bars and other processed foods are discouraged because they have ingredients that are not acceptable, especially on Induction. One every once in a while should be okay but try to avoid them as much as you can. I wouldn't eat more than one per week, if that many at all. They might stall your weight loss so I'd suggest adding them in slowly and if you see a stall cut them down or out completely.
Peanut butter is not allowed on Induction. If you're on Induction for more than 2 weeks (extended Induction) the following nuts can be added in: almonds, brazil nuts, cashews, hulled sunflower seeds, macadamias, pecans, pistachios, and walnuts. If I recall correctly, Dr. Atkins recommended macadamias and almonds as the best nuts. Peanuts are considered more of a legume than a nut and are quite carby so they're not added in until much later. If you must have peanut butter, make sure it's organic without any added sugar and don't eat more than a tablespoon or two.
Full-fat dressings are allowed and even encouraged! Make sure to count the carbs and check for acceptable ingredients.
The best thing to do is just see what works for you. If you haven't read the book yet, then I suggest reading any copy dated (2002 or before? someone correct me if I'm wrong) because those were written by Dr. Atkins himself. The best thing to do is just experiment--things that stall some may not stall others. When researching about the bars a while back I read about people who ate them a lot and still lost weight, while others could stall just by looking at them.
Good luck!