Most nutritionists will say that chocolate (whether Hershey's or any other) brand does not cause acne. These, however, are the nutritionists who have not suffered this themselves.
Everybody's physiology is different, and there are accounts of some people being unable to eat large amounts of chocolate or chocolate products without suffering effects of acne. It would also seem that, the more cocoa used in the production (e.g. darker chocolate) the more pronounced the effects.