There is an option in the vBulletin AdminCP to delete any account at any time, you can do it in batch.
You can delete all members with a certain post count, all with a certain post count or lower, all who joined before or after a certain date... ... this was possible in a vBulletin admin panel demo I used a few months back. No hacks, mods or anything required. I notice that most of these accounts in question appear to have joined a long long time ago and many have no posts... these are candidates for deletion? Like I have said, the default options allow for this.
If you find the default options are not enough, you can always execute a custom SQL query to do what you like.
I think David's comment that it may not be possible is due to logistics rather than the facilities not existing. It may be too much work and difficult to implement, but literally impossible? I would say no, there is always a way to do something like that.
