There's nothing about drums only the drums were just an example, drag import will work on all the midi tracks.
You may be using a pg midi drums track but want to enhance it bit so you just drag a drum solo/fill/roll in at whatever bar you need and it will overwrite the existing midi or merge with it.
Like if you are using free MT Power Drummer or free DrumMicA you can drag the midi drum section out and into the piano roll.
http://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=459905#Post459905