Move all accounts with certain Drupal role into CIviCRM group
If you're feeling brave, and you've got a test site to try this out on first, this should be doable almost instantly via a SQL statement.  

To simplify this query, first look up the group ID (SELECT id FROM civicrm_group WHERE name = 'Spam Group') and the Drupal role ID (`SELECT rid FROM role WHERE name = 'spam account').  

Note: If you have separate databases for Drupal and CiviCRM, you'll need to preface references to tables with the database name.  I'm assuming some basic SQL savviness here - my apologies if this isn't helpful as a result!

Once you have the role ID and group ID (we'll assume "12" and "23" respectively below), do the following:

INSERT INTO civicrm_group_contact (group_id, contact_id) 
SELECT '23', civicrm_uf_match.contact_id
FROM users_roles
JOIN civicrm_uf_match ON uid = contact_id
WHERE rid = 12;