I don't think there are any differences in dimensions between Golf/A3 bearings
and S3/TT bearings, just a completely machined surface.
Also my track width doesn't increase with the S3 (3C0...) hubs (fortunately).
No doubt without any dust cover the rotor will cook the ball joint which
has an inner plastic lining and is filled with grease. This will shorten it's life
significiently.
I'd recommend to protect the ball joint by bending a small piece of sheet
metal on it.
Bend yellow parts 90° to protect the ball joint and the green around the the steering rod.