If you take the UBB smilies and put them into the root level of the new BBS HTML pages, it should work. The old software wrote code to load the images from the same directory as the HTML page (that's what'll happen if you don't put a pathname in the img src tag). So it seems like it should still be doable without changing the database.
I don't know what the BBS directory structure looks like, or what the old UBB smilies were named, so I can't give any more specific advise than that--but from looking at the HTML generated by the BBS page, as long as the old UBB smilies are in the same directory, the browser should be able to locate the images.