Apology as I miss read your post a little.
The PDX notam you quote is not associated with low vis. This is applicable to a Cat 1 ils downgrading to less than cat 1 do to unservicability. Probably some new construction screwing up the beam.
The ORD is a declaration that the runway qualification is downgraded.
That's fine. It means that if low vis is in force it will only be declared cat 2 at best.
A declaration of cat 2 does not however mean that if your equipment and crew are qualified cat 3 you can fly cat 3 minima without the runway being declared cat 3 ops.
One cannot simply assume the state of the ground facilities.