Is there any Taleo system user account list?

Customer are now reviewing their company user accounts in Taleo with using OBI report, they found that there are some user accounts which are found in OBI report but cannot find in SmartOrg User Account. So we want to ask:

1. Are those accounts "System User Account"? Is there any list for the system user accounts which used by Taleo or Oracle?
2. How can we search those accounts in Taleo?
3. Is those accounts are useless, how can we inactive or delete those accounts?

Thanks.