I would weight a high DAT more heavily in importance than a high GPA. And the GPA number is more important than where it was earned.

That being said, BYU puts out a gazillion more dental students each year than any other undergrad program in the country -- well beyond simply having a higher student body size. Last I checked it was ~ 225, with the next highest school around 50. I expect it has gone up since then. At my dental school, UMaryland, there was some consideration given to where the applicant's GPA was earned, although I suspect is was down the list as a tiebreaker.

There were certainly grad students that did well coming from all over, but we had a decided overrepresentation of BYU students in all seven classes that I observed (three classes that graduated before me, and the three that had enrolled by the time I graduated, as well as my own).