It would be reasonable to assume there would be at least one quest solution in each BF dungeon, but they really are distributed randomly, so you could have most third levels of dungeons empty and 4 or 5 quest items or monsters in the same dungeon.
The general consensus in the forum seems to be that people who clear the BF dungeons would like some type of boss monster at the end of the dungeon (as motivation / reward for getting through the earlier levels), even if it were not quest related.
