There will be surface rust on anything that sits for more than a couple of days (non-automotive example: railroad tracks). But that gets scrubbed off the first time the pads hit discs. The Leaf pads will hit discs at least once on every trip, coming up to a stoplight if nothing else. In your case, if the caliper is stuck and pads never hit disc, I could see that being a problem.

But to directly answer your question: looking at the discs through the wheel spokes, they're still nice and shiny so I'm going to assume that it's not a problem. I suppose it's entirely possible that Nissan accounted for this and rejiggered the content of the discs, but I don't know one way or the other.