Well the reasons parents homeschool probably has nothing to do with music but it doesn't mean their kid can get a space in the band. It's probably not acting but they can't star in the school play.
To me it seems kind of petty to say you have to take it all or none. Most the time the reasons parents homeschool have nothing to do with sports. So we tell people that they have to pay the tax bill for other kids to play sports but their kids aren't allowed to play because.... ? It seems to me like people just want to punish these kids in some way because their parents choose to homeschool. If there is a pass or play requirement that is easy, the parent(teacher) needs to sign a statement that the student is passing.