Tropical hibiscus dies in the winter, and hardy hibiscus goes dormant in the winter at about the time the temps drop to freezing. Once dormant they loose their leaves, It is just my opionion, but I would think that they would have to be pretty mature for their bare branching to grow thick enough to provide much screening.

There is a house along a busy street near where I live, which has a row of mature rose of sharon bushes growing along their privacy fence on the street side. I do not remember what effect they make in the winter. As soon as they drop their leaves this fall, I will respond again and let you know how well they are screening the view of the privacy fence along which they are planted.

You might want to think about liliacs for a hedge. They get to be about 12 feet tall and make a really good hedge. Rose of sharons will make a hedge, but they tend to be a little busy on the top and less at the bottom. so if you really want to screen this lawn from your view, the rose of sharon hedge may not work as well. Liliacs are easy to start, because they send up so many sprouts out from the base. You can probably get plenty of starts from people that have them. That is why they really make a good screen. Good luck!!