First, I do not use RealBand, because I already knew another DAW years before. Second, I don't know anything about running BIAB and RealBand together in real time.
However, I think if you are asking if there is anything else RealBand can do that other DAW software cannot, besides loading in BIAB files, the answer is Yes. RealBand can regenerate tracks in the same way as BIAB, so you can keep trying for a track you like.
Here's a link to the video introducing RealBand:
http://www.pgmusic.com/realbandvideos.htm