Not sure how old your guidebook is. Up until a few years ago, the only way to get in to BB was to make a mad dash at park opening and hope for the best. They do now take Priority Seating requests. Most of the time you'll need to call well in advance. It has become more and more popular. There are still the rare occaisions when you can get a table same day, but not very often.
And yes, the BB is always closed when Pirates is closed. It would just ruin the whole atomosphere to either look into an empty river or have a huge tarp along the edge of the restaurant.