In my opinion, Oracle exports by themselves are not a good backup strategy. An Oracle export is a snapshot in time. You will not be able to recover any changes since that export was taken. Oracle exports can be used to do something like restore a table that was accidentally dropped. But for the most part, a good cold or hot backup is preferable.
I would strongly recommend purchasing a copy of the Oracle 9i Backup and Recovery Handbook by Velpuri & Adkoli on Oracle Press. This is a must read for Oracle DBAs who need to implement solid backup and recovery protocols.
But to answer your question, if you lose your database, to recover the database from an Oracle export dump you'll have to delete your database from your server, recreate a shell of a database, and import the contents of the dump file.
This was first published in October 2004