Yes, this is certainly possible. You are right, it’d be a struggle maintaining it in two places, especially at that size.
You have two options, you can export from your existing database and create a custom labelled CSV file containing your database info. You’d have to map column names to fields, i.e. post_title and post_content and so on. Then you use the WordPress Importer plugin to import your CSV as posts into WP. This option would of course need you to export from database #1, convert to WP importable CSV, and import into WP every time you want to update both in both places.
Second, preferable option would be to connect directly to database #1 from your WP installation. Then you can change the Explorable themes query of the WP database to simply PHP loop through data from your original database.
Email me if you need assistance with this, http://rorymorris.co.uk
