Welll...I have anecdotally been paying attention to this in the meet programs to entertain myself during college gym meets in our area. Granted, the college team here is a very good D1 team. But, it appears that over half of the girls do seem to homeschool. However, that being said, many of the girls were elite gymnasts who dropped back to 10 for college gymnastics. The more disheartening thing than the school piece is that it appears you almost have to go elite at least for a while to be competitive for a college team.
This is true of the top D1 teams, but certainly not most teams.