Yes. The "RealTracks" and "Drums" folders, which are normally located in your /Applications/Band-in-a-Box® folder, contain all of the audio files, so if you have a lot of RealTracks and RealDrums these folders will be quite large. Moving them to a different hard drive allows you to free up disk space on your system drive if you need to. To move them, you can simply select those two folders and drag them to a different location. This may take a while to copy, depending on how many RealTracks you have and how fast your computer is. It is also possible to install these folders to a custom location if you choose the [CUSTOMIZE] option during installation.
You don't need to worry about moving the 'RealTracks - Demos', Drums - Demos', or anything other folders; these folders should stay in the Band-in-a-Box® folder.
Either way, you need to specify the location of the folders in Band-in-a-Box® before you will be able to use them, if they are located anywhere outside your main Band-in-a-Box® folder. To do this, go to Windows | RealTracks, and Windows | RealDrums and specify the custom location in the Preferences dialogs.