John Wittenberg :
http://www.extremetech.com/latest/223320-demystifying-directx-12-support-what-amd-intel-and-nvidia-do-and-dont-deliver?origref=
Very first Google hit for DX12 graphics card.
TLDR - Yes, basic DX12 features will work for all those cards. BUT none of those will support all the extra DX12 features - only the 900 series for Nvidia will support every DX12 function.
The thing is, we don't even know if dev's have any plans to support any of those new features. What we do know, is they do plan to take advantage of the low overhead API, which will benefit everyone with a reasonably up to date card. If the past means anything, we can expect the wave of DX12 games to stick with features most everyone can use.