Having used Proactiv in the past and now own a Clarisonic; they would work well together. Having said that, I would get the brushes for sensitive skin in the beginning. I over did-it with my Clarisonic when I first got it. I don't have sensitive skin and still had some trouble. Hope this helps.
I used to have proactiv and now I own a clarisonic. I wouldn't reccomened using the clarisonic with the proactiv cleanser as it has exfoliating beads, and that combined with the pusles of the clarisonic might really irritate your skin- especially if you have sensitive skin. If you're going to get a clarisonic, try to only use it with "liquid" cleansers because it will be more gentle on your skin. Hope this helps!
I have used the Clairsonic with products with exfoliating beads with no problem. I've done this with the regular head that comes with the Mia. If you have sensitive skin, they have two different heads that you might want to try: the sensitive skin head as mentioned by another poster, and the delicate head, which is even more gentle. This seems like the kind of thing you are going to have to try yourself to find out what works for you. If you look at the reviews on the Sephora website, different people have widely varying experiences using the same technique/products. But if you already know that your skin is sensitive, I would try one of the softer brushes with your proactiv.
Hope that helps!