I'm not entirely sure I understand your question, but here are a couple of reactions I had to your post that might be helpful:
- You may not need to use events at all. CiviVolunteer provides a number of interfaces for creating volunteer projects, advertising volunteer opportunities, reporting on sign-ups, etc., that you might be adding unnecessary complexity by incorporating CiviEvent into the mix.
- If there are good reasons for using both CiviEvent and CiviVolunteer, you can add a little CSS to your event info page to hide the "Volunteer Now" button. Direct your vetted volunteers to register by going to http://yoursite.com/civicrm/vol/#/volunteer/opportunities. (URL assumes it's a Drupal website. The pattern will be a little different for other CMSes, but you can find this link by going to Volunteers > Search for Volunteer Opportunities in the CiviCRM menu.)