I would advise caution and to only do so if you know how to really control your privacy settings on Facebook. I would not recommend allowing them to be on a friends list where they see all the personal details of your life, what you like, what you post etc.
If you have them as "acquaintance" and set it up where your personal posts only go to "friends" and more generic stuff to "friends and acquaintances" it could work.
As a general rule, I'd advise against it. I don't think most bosses add their employees unless they are snooping honestly and who needs that hassle?