Hi Diki
The VST plays the sound yes, but it is controlled by the OAS software, therefore if the notes have to be stopped and then retriggered to prevent dissonances, then the OAS software will tell the VST to stop playing the sound and then retrigger it.
I have included a link to the OAS 6 Programming guide (The version I still run) however I believe it is similar to OAS 7. (The trigger function has I believe been available since the launch in 2000, or at least OAS 4 (2002))
The OAA (Open Art Arranger) however takes the acc section beyond a whole new level.
The style section starts in chapter 10.
Hope this helps

Bill

http://www.4shared.com/file/33114991/3ed74219/Programmers_Guide-OAS-6.html