I didn't realize I could do that!
Just did it - he's right, he has no messages. I was able to send a message from him to me, and then I could respond back and it showed up in his account. But when I sent a message to him, it didn't go through, and on my acct, it said I was the only participant.
Edited to add that I checked his preferences in his account, and he is set up to accept PMs from other users. I tried setting that again and updating it in case it was just a glitch, but it still didn't work if I PM'ed him first.