Pretty much. It is meant to rust, and once that outer layer oxidizes thats it, its not going to continue corroding anything.
However...it can and has stained sidewalks before.
It's New York City. I really don't think many will notice...or care.
As an aside, I went through Brooklyn a couple days ago—the majority of the time I stay on the freeway to the LIE when I'm up on Long Island, but this time I chose to take the scenic route, straight downpast Atlantic Avenue—and went straight past this place. It's an interesting-looking building for sure, but I can only assume that some other buildings are due to go up around the Barclays, because right now the shape and design looks kinda out of place with the rest of downtown BK. (And am I the only one reminded of those old HBO movie opening sequences when I see this building??)