I was asked to write a letter once. The guy had his license suspended for a DUI and still drove to meetings and I suppose everywhere else as well. I asked him if he wanted me to be honest. He said "yes!" I told him I'd have to say that I'd seen him driving to meetings. He said, "forget it."
Be honest. If you can't say something honest and accurate, don't say anything at all. There are others who know him better. You need to live with yourself.