They do grow in the hills outside Melbourne, and they do get frosts there , but I believe that may be a 9a not 7a. They need very good drainage.
I suspect they wont grow in 7a

I don't believe that there's any variety of protea that can grow outside here (in MD).
Karyn

Thanks for answering! I have done a little research, and I believe I have found a few that are hardy enough. It seems that both Protea dracomontana (Drakensberg Sugarbush) and subvestita (Waterlily Sugarbush), along with both Grevillea victoriae (Royal Grevillea) and juniperina (Juniper Grevillea), and Embothrium coccineum 'Lanceolatum' (Chilean Fire Bush) should be able to bear the winter. Also, I have just got a tip that Lomatia myricoides should be hardy enough. I'm still trying to find out more information; anything will help!