Rikki, yes I am certain that you will find drums on channels (or tracks with different numbers) all over the place in Yamaha Styles. It is true, however, that drums are mostly on channel 9 and 10. Just as an example, take a look at an unmodified 9000 Pro BigBand Style (Channel 2, 8 & 10). In some styles some of these channels (not tracks) are empty (drums loaded but no messages.

So to make a separate VST for drums practical I would recommend merging drums into two channels say 9 & 10. This gives you the option of using something like a Jazz Kit together with a Brush Kit. This is easy to do with M. Bedesem's StyleMaker partnered with Sonar (or any other sequencer). I like Cakewalk sequencers because of the availability of instrument definition files.