Basically - yes and no
No one is going to arrest you and throw you in dukan jail for eating a muller as a tolerated item.
But you take the risk that you may stall if you start relying on them as a daily treat, and you will almost certainly stall if you start eating 3 a day, as I have seen on some menus in the past.
Confession - I eat two a week, usually mixed with zero greek and frozen, or in a muffin batter.