Pretty sure he hasn't, at least not the later chapters, he seems sane from his appearances on this forum.
And yeah, if you look around in Daz3D games you will find a lot of "cousins" across games since there are only so many models but thousands of games. Specifically "Dee" has been reused quite a bit, as Nemo said, sometimes intentional as an hommage or parody, often not so. Personally I find Ashley and Dee not even that similar. Sure, blonde small girls with well rounded big ... uhm ... "characters", but apart from that I can think of worse offenders.
Personally I have more problems with the hair of some characters looking too much alike (not so much in this game, although Sophia's haircut has inspired dozens of wannabe cuties - the problems of fame I guess). It is often way more obvious and can be less mitigated just by some sliders.
Then again, if we can believe that the same "model" of an actor in the movies can be a complete loser in one movie and the envy of the town in the next, I think we can get through this as well.