It depends, Julie. Dogs who consume enough cocoa bean shell mulch could potentially develop signs similar to that of chocolate poisoning, including vomiting and diarrhea. In cases where very large amounts of mulch have been consumed, muscle tremors or other more serious neurological signs could occur. To date, the ASPCA Animal Poison Control Center has not received any cases involving animal deaths due to cocoa mulch ingestion.
One key point to remember is that some dogs, particularly those with indiscriminate eating habits, can be attracted to any kind of organic matter. If you have a dog who tends to be, shall we say, less than finicky, it is important that your dog not be left unsupervised or allowed in areas where such materials are being used.
In case you have not already seen it, please read this article (.pdf) on our website that provides additional information on cocoa bean shell mulch.