The nightingale hood works without beards. There's no reason wearing a masked cowl could disable the beard model for the duration of the helmet being worn.
That's because it disables the entire head. You can only do 2 different things:
1)Disable hair (like for hoods, non-full helms, DB cowl,etc.)
2)Disable head (like for closed helms, Nightingale hood, full masks.)
There is currently no way to disable beards without disabling the rest of the head model.