i think yes, but then again no...
so i think if it is really serious relationship, you should, but always keep in mind people makes mistakes in the past, and the past can be undone...
its good to be open, and i would believe yes you should know...
i don't want to find it out one day on my own. at least i know then and doesn't hear rumours of a 'bad past' cuz usually when stuff like thats gets into the open, it gets nasty....