In reply to nation1:
Just occasionally there's a gardien at the hut - maybe at the busiest time of the season or just randomly, I'm not sure. When I stayed there I certainly didn't book it - I don't think there was any system in place to do so, but this was quite a while ago, when the little Savoia hut was still there as well. You might be advised to just check that this hasn't changed with the tourist office or the guide's bureau in Cervinia. I'd imagine there might be more people doing the Italian ridge this year rather than fork out 150 Swiss francs per person at the new Hörnli!