You would simply take one of the existing forum integration files that closely matches YaBB (something I've used in the past, but its been a while) and then modify the queries to match the data from that board.
Others have done such integrations and you could even submit it to us for review and inclusion should it work properly. I don't know of any hurdle that would prevent you from doing such an integration in just a few hours if you've done them before.
Please do not PM me for support or sales questions. Thank you for your understanding.