Relevant Versions: 7.0 and up
Yes. The Administrator account is a special account. It does not use Active Directory information. If Active Directory authentication is enabled, all other users must have the same name within Vontu as in Active Directory.
AD usernames are not case-sensitive, but Vontu user names are. For example, you have an active directory user "John" that is then added to Vontu. He will be able to log into his desktop as "john" or "JOHN". However, when logging into Enforce, he will always have to use the username "John". All other variations will result in authentication failure.
EXCEPTION: In order to get this feature to work, you must disable and re-enable AD Authentication. A bug report has been filed to eliminate the need for disabling/re-enabling active directory authentication (E-track 1449383).