A program can only interview a fraction of applicants, so there needs to be a filtering and GPA is likely a factor. GPA/class rank is likely a more important factor at the more competitive programs.
Yes to a certain extent. If you have a low GPA and not a lot of extracurriculars to make up for it (research, clubs, service, etc.) then you're at a disadvantage. However, being peds myself, if you have good experience after dental school (GPR, private practice that sees a lot of kids) then that would make up for the lower GPA. For peds, the more experience you have with kids, the better,
Some programs do. A lot will depend on the PD, and how important the in service and board scores are to them. For PD's that like to brag about high scores and board passage rate, D school GPA will undoubtedly be a large factor. Past performance as a predictor of future success. I hope that answers your question.