I went to two IBD medical conferences (2007, 2008) and this topic was discussed there. They (experts from Mayo clinic, Cedars-Sinai, et al) all felt that the meds were safe for conception -- except methotrexate. I could probably dig up the studies they referenced but I don't have the handouts on me right now.
By the way, I'm a male - but no kids.
I'm a 38 year old male with one child. I was diagnosed 8 years ago and was told that the prednisone I was taking would lower sperm count. I never asked about 6MP, but I wasn't taking it at the time. Now I take Imuran but I'm also finished having kids :).