Exclusive Office 365 user provisioning:

With the latest release of ADManager Plus, version 6600, you can create accounts for users only in Office 365 without having to create accounts for them in Active Directory.

Select the 'Office 365' alone option during user creation to create individual O365 accounts independent of AD. 

Separate UPN for Office 365 users: 

You can set a separate User Principal Name for Office 365 user independent of any of the AD attributes (email address, logon, etc). If the UPN is not specified, the logon name will be considered as the default UPN.

Manage more Exchange Online attributes: 

Office 365 properties now comes with new attributes such as E-mail Alias, Litigation Hold, In-Place Archive, and Group membership for configuration in both single and bulk user creation, and in 'Office 365 account creation for AD users' under  'Office 365 management' tab.