I have used almond bark before to dip these but found that the candy wafers work better. Sometimes when you dip the balls the Oreos can leave some crumbs in the coating but the wafers tend to do this way less.
I like to divide my coating into half or fourths so that if for some reason dark oreo bits get in one bowl you have others as back up. You can even dip them twice. Once in a layer and if it has oreo bits, oh well. The second time dip them in a fresh melting coating bowl and then there are no crumbs to worry about. I only had to dip these once but in the past I've had oreo bits sneak in my white coating