Turns out there might be a way to do this, albiet a very tedious way. But once it's done, if it works, it's done.
You should be able to just move the instruments folder of a third party library to you Kontakt Factory Library folder but you will get a "cannot find samples" error dialog when trying to load it via the Libraries tab in Kontakt. Then you can just point Kontakt to the drive/folder where that libraries samples are and, hopefully, be good to go.
For me this means doing this about 25 times.
Plus, as some have alluded above, the Libraries tab in Kontakt is no great browser anyway.
We'll see.