Is it true that Dawn dish detergent maybe used to reduce back acne as it breaks up the oil that can cause break outs?

If the Dawn dish detergent is in it's diluted form then it would be safe to use. As for it's effectiveness, that would differ from person to person. Yes, it would dry out the acne and possible reduce the oil. However, it would also dry out your skin, so it would be wise to use a moisturizer as well.