I take it you don't see the need for them being removable and I can see your point. It does make me wonder if the customer ever took them off.
I figure that having them plug in shouldn't be a problem since, you can always just leave them in and pretend they are not removable, so my inclination is still to not glue them in/on. I'd just as soon not have them there when final sanding, finishing, and even if the instrument ever comes back for refinishing having them come out seems like a plus. I have not done so, but I could also imagine the sockets as a really clean way to attach a possum board.