I use folksonomy tags/genre tags with Picard, specifically I enabled the option to use all folksonomy tags as genres (because there are some that aren't proper MusicBrainz genres yet). I then used the include or exclude features to exclude the non-genre folksonomy tags (e.g. "sillyname"), and to fall back to the artist genres if no release or release group genres are found.

When I have a release tagged as just "sillyname", the genre list ends up empty, and does not perform the normal fallback. Personally I would expect the fallback to occur when the tags for the release end up empty after the filters are applied, not before.