Yes, with DBPowerAmp I can go into an album folder, select every song (ctrl + A), right-click and select properties. There's a tab that lists the tags and you can edit the ones that apply to every song such as artist, genre, year, etc. Once you clean up the tags you'll probably want to delete/rescan your library. Maybe it was just an old version of the server software but the Squeezebox had a tendency to remember the old tags if I didn't do a complete rescan...