The only thing that I've been able to dig up on it is that its not recomended to use as substrate if you feed inside the enclosure. The reason stated is that it swells slightly when ingested. If too much is ingested it could cause impaction problems. (I feed in a seperate enclosure) In fact.. I found a couple people talking about using a 'forest floor mix' that is made mostly of cocoa shells for their Gaboons.
I'm still not thinking its safe to use... This is just what I've been able to dig up on it so far.