Mudflaps would have worked just fine for the frequencies that they support just as loop and bowtie antennas will work with UHF DTV stations today (assuming they have enough gain). For more than a few, the transition to DTV meant that most of the VHF channels went away. Now in the face of our third repack, the antennas designed to include 600-800MHz frequencies are a lot less interesting.That's why we had all those mudflaps and funky looking plastic antennas emerging after the digital switch, right? A mudflap wouldn't have worked for analog I'm assuming.
The modulation scheme is of no interest to an antenna as it grabs the carrier at that frequency. If they switched polarity from horizontal to vertical, you'd just turn the antenna on its side.