Yeah,
but if you do that, all you're really doing is adding a new (or adding new items) to an existing vault (via the archive itself). Its kind of a simplistic way to look at it, but I always teach people to think of archives as the "index" of the source (be it files, mailboxes, etc), and the vault stores as the db and storage on the backend. Pushing to a new archive doesn't change the backend store or db's (which I think is my meandering point).
Truth be told tho, I usually always recommend that the pst's fall in tot he general ingestion email vault (if you've set that up correctly) so that SIS has a chance to work on some of those items. Course, SIS being SIS,...you're rolling dice depending on how your environment is setup and what the content actually is.
micah