Legally he cannot. However, for all practical purposes until his employer has documentation (the QDRO) stating that the account has been divided he CAN withdraw the money and do who knows what with it. He would be stupid to do so, because not only would he have to pay tax on the money, but he would also have to account for it when you took him to court for contempt.
However seriously angry people have been known to do seriously stupid things. You asked if there was anything that he could do to mess it up...and that's something that he could do. Hopefully, he won't be that stupid.