I honestly haven't a clue. I googled it to see its composition, and it contains 12g carbs for 200cl (whereas semi skimmed 9g carbs), and of course the fat content is far higher...
Do you eat yoghurt or other dairy?
How much milk would you usually use in a Dukan day?
That makes sense - lactose is usually converted into lactase in the process of making cheese, yogurt etc, and lactase is much easier to digest.
On the question of semi-skimmed, I can only offer my own experience. We have semi-skimmed milk in the office, and I would sometimes use a dash of this in my office coffee or tea when I couldn't face it black. I didn't seem to slow down my weight loss.