Greetings @Traveler, sorry, couldn’t resist:)
Thank you for the post and welcome to the forum 
Just checked and this has more to do with the special status of the “Fonts” folder (even in Windows you might see it with a special folder icon). An ordinary hidden folder containing fonts can be added into FontBase no problemo.
I’m afraid the app isn’t very suitable for dealing with the fonts that are already installed on your system and are always active by design.
Hope this helps,
Yuriy
FontBase Dev Team