Yes you can manually input jobs onto your JobRoller site if you wish. If you would like an idea of the theme is installed and configured, you can have a look at the
JobRoller documentation here.
Indeed.com integration is already built into JobRoller, and there are other job feed aggregator plugins available in the
AppThemes marketplace, however these all work in the same way in that listings are not actually saved into your WordPress admin dashboard, they are dynamically displayed on your site and ultimately linked back to the site. Thanks.