I have 3 staff working for me and they are all on Facebook. I haven't added them because as a boss and company owner I'd prefer NOT to know. But to be honest perhaps people should think twice about the shit they post of Facebook, after all it is a public site by default.
With regards to Safeway I'd ask to see a copy of their policy regarding this. Being a big company though you might be shit out of luck, they may be one step ahead as it's a growing trend.