Hi.

At some version Amarok does not use SMB/NFS backends for collection and should see these folders automatically.

I don't find my NFS-folders anywhere in my Amarok 2.8.0 though. And adding them to local collection manually just causes re-scans etc.

So how should it actually work?

Well, it doesn't show them as a separate collection if you expect this, it never did. What you can do is add a Samba/CIFS or NFS share to the local collection. Those will be read when they are mounted and available.
There still is a Solid bug preventing NFS shares to be read correctly, though: https://bugs.kde.org/show_bug.cgi?id=328808

If you mean adding the mounted folder to ordinary collection, then it is not very good option in my case. The share is behind really slow connection and there are very many files. So the scan will be running basically forever.