While a cute ideal, mechanically I wouldn't do it. You loose alot of the benefits of a typical divided tank & then you loose some of having separate tanks as well. Simply put a divider should allow water to flow freely or should not allow any water to pass through at all. This is just going to restrict the water flow negating the stability advantages of a divided tank. Also would require separate filtration & depending on the size tank different heat as well. But because it is not completely water tight then it will not stop disease or other issues from traveling across the tank.
Also as was pointed out above. There is no real problem letting them see each other. I have 6 males that were at one time or another able to see there neighbor & they all flare on occasion for a few minutes, but then stop. I have not had any of them that just flared non stop.