I'm getting married in 2 months. Way back several months ago, my MIL who by way of it being a small world happens to know my dad's boss, inadvertently invited my dad's boss to the wedding. Not officially or anything but still no mistaking it and very public, so now I'm obligated to invite her.
My dad was PO'ed. Now mind you he gets along with his boss just fine, and has socialized with her and even invited her to parties of his own. And yes my dad is paying in large part for my reception. But he felt that its my (and my DF's) wedding. The friends of his that are being invited - and there's lots - are ones whom I know, and who have been in my life, and who I chose. The friends who we spend Christmas with, or who were always around the house when I was kid, the ones who would recognize me if they bumped into me on the street and who know enough about me to have a bit of a personal chat.
I think its totally reasonable to invite what are essentially family friends - sure closer perhaps to the parent, but ultimately a friend of the family unit as a whole. Employees with no relationship to the family but only to one member, a member who is not actually the one getting married, I think is an inappropriate invite.
IMO a wedding should be about showing love and support and affection for the couple getting married. A don't think an employee of one of the parents fits that emotional role.