FYI, different enzymes are required to digest bones & protein versus plant material...VERY different. Snakes are not & cannot be 'vegetarians' for this reason.
It's not about being "tough enough to digest bones"...they do not possess the enzymes needed to break down plant material.
I too would be concerned about mulch with splinters...perforated guts are not unheard of, but usually minor amounts of debris just "go along for the ride" OK.