But I still hate to see a company policy stop 2 people from loving each other. The intelligent thing however would be for 1 person to quit the company and work in a different company.
I guess a reasonable company would have the policy "it depends" and make sure that each case is judged on it's own merits, and that no one would just get fired - in some cases just maybe offered a different position.
I worked in one place where the wife of the CEO worked in a non-managerial role far from any top level management. Wasn't a problem, and she was the first to loose her job when they had to downsize. Totally unfair to her since she was a top performer, but that's the only way it could be handled I guess.