We are kind of in the same boat. My husband has been on azathioprine and we just found out we are having a baby. We hadn't heard anything from his GI doctor about there being any problems with it, but when we researched it on the internet...I kind of freaked out. I have ready almost every piece of literature out there and it looks like only one study is cited as to the reasons a man should not be on the medicine while trying to have a child.
It helps to know that someone out there has had a successful outcome!
We talk to his doctor on Monday so hopefully he will have input.