Better safe than sorry, any mulch can cause problems if ingested. One of our basenji friends used to deliver blueberries to us from the Hersey PA, area every summer and he always brought us a load of cocoa mulch for our beds. I had most of it in the front yard where the dogs did not have access, but did have some spread around a bush in the dog area, they never paid any attention to it.
Just an aside, friend has Golden labs + turtles. She uses 'blood mulch' for the plants she uses to feed the turts. One of the Goldens had 'blood' in her poop
for quite some time, vet visits and several dolars later, guess what…darn golden was getting into the mulch behind everyone's back and it was, of course, making it's way through, and looking bloody and bad. Having been an e-mail participant in the concern, I had to just laugh. No harm, No foul, just a dog being a dog. Dog is fine, mulch is out of reach now, and the turts are OK too.