I am fairly sure that caseine is a problem for acne. However, the real test is for you to take a month off of dairy and see what you experience. You can continue the cultured products, and should eat more of the organic plain yogurt. The fermentation of the yogurt chemically changes the caseine so it is not a factor.
I am now understanding much more of the "whys" behind things like this, but I mostly know caseine and gluten are Acne instigators because of my experience. I'm sure from person to person the factors change slightly. I'm no doctor and no expert.
It sounds like your bowels are pretty regular and that is great.
If you could tell me how old you are and what specific kind of Acne you have, that would be interesting. For instance, is it blackheads or pimples? All over the face or localized in the middle third of your face? Oily skin or not? Any Acne on other parts of the body like chest, back, or backs of arms?