Yes, Likewise Software does do Linux Active Directory integration so you can join Linux workstations and servers to Active Directory, which would allow domain accounts to log into Linux systems. In turn, user accounts can be managed in one centralized location. This is all part of the Likewise Open solution, which is open source and free.
However, the Administration Console for Linux is part of the licensed Enterprise solution which, like you said, is not free.
Let me know if you have any questions regarding Likewise Software, though.