This is one of those things that nobody really agrees on, but I'll try to put in a moderate point of view...
As an engineer, and generally scientifically minded person... I would not use anything but steel for the fire basket, b/c I know it gets hot enough to oxidize pretty much anything (including zinc). That said, if you look at the pics of my UDS, it has lots of galv hardware pretty much every where else. There are lots of detailed threads out there describing how zinc oxidizes at over 700-something degrees. Unless it's the fire basket itself, I have a hard time imagining that you will ever achieve 700+ degrees with your other hardware. There will be some that throw caution to the wind and say the galv. concern in a myth. There are also others that won't even buy cars with galvanized parts (I joke of course). Anyway, I think I'm fairly moderate on the issue and hope that helps the concerned posters above.