Allain's advice was to launch NitroPDF.exe with a compatibility setting to override default high DPI scaling. That did the trick. All PDF text now renders without pixelation/fuzziness. Thus, ClearType isn't even needed - which is good because NitroPDF doesn't utilize it.
The specific steps he provided are:
1. Right-click Nitro Pro desktop shortcut or the NitroPDF.exe (by default is installed in C:\Program Files\Nitro\Pro\12) then select Properties 2. Nitro Pro Properties window will open, click on Compatibility tab 3. Under Settings, click on Change high DPI settings.
4. Another Nitro Pro Properties window will open.
5. Enable Override high DPI scaling behavior.
6. OK > OK to save the setting and test Nitro Pro again.