I long time ago I wrote a acticle mdt-automatisch-updates-via-wsus-laten-installeren-tijdens-het-deployen-van-het-os (Dutch) about using wsus with MDT.
After you deploy a Windows 7 SP1 machine updating takes a lot of time.
How you do this: It’s quit simpley. Import de WSUS Content in to Packages.
The error is normal because not everything is imported.
Delete every time you do this. Update & Hotfix packages. If you don’t you will end in a error state when you deploy a machine.