According to Desktop Window Manager is always on (Windows) on MSDN:
In Windows 8, Desktop Window Manager (DWM) is always ON and cannot be disabled by end users and apps.
In Windows 8, DWM desktop composition is a core operating system component and cannot be disabled. With a few exceptions, desktop composition is always on; it’s started before the user logon and remains active for the duration of a session.
All of the options for disabling desktop composition that exist in Window 7 are removed
Apps cannot use DwmEnableComposition to disable desktop composition. In order to maintain backward compatibility, a call to this API will return success; however, desktop composition is not disabled
Well, there's a pretty definitive answer. I'm somewhat curious what the "with a few exceptions" refers to, though... please add a comment if you happen to know. :)