Not really because his body will adapt to the on coming blow from the sword by making his skin metallic or something hard enough to withstand it but the only ways he could get harmed by the bone sword is if he's adapting to one thing already while the bone sword impales him after. Meaning, he can adapt to one thing at a time and also if the attack is too fast to react to. Meaning, if your character was to shake his hand and bring about a surprise attack, his body may not react in time to protect him. 

And also if he was to swallow something his body could not adapt to.