I was recently flying ZQN-AKL (all-Y config) and they announced preboarding of OW Sapphire's and Emeralds. I'm sapphire (AA Plt) but I forgot to give my FF # at check-in, and I don't have a card yet either, but the agent said to just go ahead. Those Kiwis are friendly! Probably didn't hurt that nobody else got up for preboarding...
But regardless of that experience, your Ruby status should show up on your boarding pass when they enter the FF information, as Kiwi Flyer said.