Bel,
Errr.... No.
CatIIIa most definatley DOES have a DH of not less than 50feet.
Alert height is not a "Company procedure", it is a certification requirement for catIII operation. It is the height below which a fail operational system will continue to a landing if one system fails.
On the 777 it's 200 feet. below this all but a few alerts are inhibited as the aircraft is certified to land after the failure of most single systems.