you guys are making a big deal of nothing. There are schools that REQUIRE a LOR from a dentist, and in which case, that dentist CAN NOT be a relative.... so obviously you HAVE to do shadowing with a non-family dentist ... end of story
For the schools that don't have the dentist-LOR requirement, then it doesn't matter what you tell them, I don't think it matters to them where you got your shadowing hours from, just as long as you have some hours.
As for reporting the shadowing hours you've done, I say do it, it is considered "dental exposure"... who cares if it came from your dad or mother, its still exposure to the field.
I shadowed my sister back in 2007, 2008, and little 2009, and last January, I started to shadow some other dentist because I needed an LOR. I didn't exactly record how many hours I did but I am estimating between 40-50 with the new dentist and approx 100+ with my sister.