Yes, and no.
Cancelling the credit cards will have a negative effect on his credit. He simply needs to call them up. If a joint account, he needs her name off the account. If its only his account(but she may have one if they sent two), he needs to simply have them send new cards with new numbers, and to a PO Box that he should be getting tomorrow.
No, he needs to cancel them and any joint bank accounts and switch banks and credit card companies. I failed to do this and 15 years after the divorce was finalized a creditor clean out my checking account. My attorney told me there was very little i could do. The bank told me that there was nothing they could do to protect any of my accounts, even those established after the marriage ended.
It was an expensive lesson.