1/ 4 way diversity (in reception, i assume), you need four “dipoles” (or rather, four series of dipoles). This can be achieved by using either:
2 crosspolar antennas separated by few meters.
4 vertical polar antennas separated by 1 or 2 meters from each other each.
2/ this kind of configuration is very old. The benefit is only that the Tx is done on a vertical polar antenna, while the Rx/Rxdiv have a polarization diversity.
But it’s useless, because if you’re ready to have two antennas on the roof, you might as well have 2 vertical polar antennas, one for Tx/Rx, the other for RxDiv.
If you don’t mind me asking, where have you found this antenna configuration ?