First of all, I have to admit that I haven’t really studied the DH in any great depth, so I can’t speak with firm authority on its validity as a theory.
But my gut feeling, based on a light examination of it, is that much of the DH is speculation. The specific attribution of particular parts of the Torah to different authors seems somewhat arbitrary and less than purely scientific. There seems to have been an orthodoxy established (if you’ll pardon the word) since the 19th century dividing up the Torah into these various hypothetical authors, and very little has changed in the DH since then.
However, that’s just my opinion of the answers that the DH posits. Its questions are extremely valid. The inconsistencies, lack of archeological and geological evidence, anachronisms, are all strong contradictions of its word-for-word divinity. And as such, it seems unlikely that the Torah came, whole cloth (or parchment) word-for-word, directly from God. It seems that there were very likely several different human authors. The DH is simply some intelligent speculation on who those authors might have been and which of them wrote which part.
The DH also usually comes with an assumption that since the Torah is not what traditional Judaism claims it to be; an exact dictation from God, then that means that God had no part of it, if there is a God at all.
I believe that despite its human authorship, the Torah is at least divinely inspired. Call it what you like – prophecy, ruach hakodesh, etc. There’s too much in there that strikes a deep chord with me and with millions and millions of others throughout history. (Yes, I know that’s unscientific, but I’m talking religion here, not science.) There was some kind of divine revelation, whether at Mount Sinai or elsewhere. That revelation may have been a single event, continuous, or punctuated, but there was something. Various authors wrote down their interpretation of that revelation, incorporating their own bises and knowledge of their own times, and Ezra later combined it into the Torah that we know today.
Again, this isn’t scientific by any means, but things like the fact that the Torah was far more compassionate than contemporaneous societies, the story of creation that seems to eerily fit our current models of cosmology (if you read between the words), and many other things help me see the divine in the Torah.
Stay tuned - tomorrow I'll post on Torah She-Bichtav vs. Torah She-Ba'al Peh