Would the KHSAA have to approve such a plan?
I don't think so, I believe this is a school district issue. I have coached in other states where various districts have had similar set-ups for other reasons. The only time I think it could be an issue would be if the coaches were to compete the teams against each other during practice but not call it a scrimmage.
I believe the rules prohibit this.
That being said all 3 schools are closing next year to make McCracken County High School.
If they will be one team in 2012, then no problem.
If they will be three separate schools this season, then i think provisions of the recruiting rules and perhaps eligibilty rules come into play.