We had a guy claim that he had some sort of skin condition that meant he couldn't shave. He wore a beard for a while. He's gone now. I don't know if he got fired, left for greener pastures or quit to pursue a bigger beard.
Anyway, the mask seals just fine around the bottom lip with most beards. I wore one in Europe as did several colleagues. It's got nothing to do with safety and everything to do with image and control.