How to use views filter on an entity property
I have now done some experimentation and find that yes, what I needed to do was use hook_views_data_alter to tell views how to handle the properties I had added above.  Here is the code inside my hook_views_data_alter function:

$data['crm_core_contact']['notes'] = array(
            'title' => t('Notes'),
            'help' => t('The notes for the contact'),
         // Information for displaying the notes field
                'field' => array(
            'handler' => 'views_handler_field',
            'click sortable' => TRUE,
  ),

    // Information for accepting a note as a filter
        'filter' => array(
        'handler' => 'views_handler_filter_string',
  ),
    // Information for sorting on a note.
        'sort' => array(
        'handler' => 'views_handler_sort',
  ),
);