I'm a little concerned because, for example, a button is not implemented as a native UIButton, and a ListView doesn't use UITableView. Instead they are composed of native UIViews with a lot of JavaScript glue.
That being said, Facebook has more experience writing iOS apps than me, so it may be possible that those things don't really matter (and doesn't preclude 1:1 components from being added down the road).
Some food for thought: what if you kept HTML and CSS but instead of using a WebView to render it, you rendered the DOM manually using UIViews? You could even make overflow: scroll; turn into UIScrollViews automatically.
<Carrousel> <Item></Item> <Item></Item> </Carrousel>
On the web you might use a div with overflow:scroll on native a scrollView.
If it's using UIViews, it isn't reimplementing native controls. It's using native controls, same as if it was implemented with (interface builder) .nib files. That's like saying "reimplementing html/css with html/css".
I've spent 15 minutes with React Native so far, and as best I can figure, the answer is no.
If they were building the GUI components from UIKit pieces, they'd get all of this for free. But I understand it would be pretty hard to get all this working with the flexible layout architecture they have... so I'm guessing they'll have to slow add all the accessibility features in over time.