The native Vive rendering (from the virtual reality supported checkbox) has been included since beta version 9 of Unity 5.4 (5.4.0 b9). I believe at this point in time this should include most things related the HMD and rendering only. If by any chance you mean native support for the controllers or other things currently unique to the vive (room scale play area) I think the current timeframe is still aways off, but perhaps someone from Unity can confirm.