Are you currently on a custom ROM? If so, they are pre-rooted by definition. So restoring a nandroid of a custom ROM will give you root, yes. But so will flashing any custom ROM on the new device or just flashing SuperSU/SU.
Even if on a stock ROM and rooted, I believe this will also migrate over if you restore a nandroid to a new device.
But in any case, root is a simple thing once the bootloader is unlocked and custom recovery is installed. It takes about 2 minutes, so whether you can migrate this or not via TWRP is really a very minor point.
Yeah I use ViperOne M8. Or do you just mean am I running things on a rooted nandroid recovery? The answer is yes to that one as well. The one I'm using now is unlocked rooted and S-OFF'd.
So basically again, I HAVE to unlock b/c that's the only way to get TWRP access, but the root can be quickly obtained via flashing my custom ROM. And of course S-OFF must be repeated because that can't be simply flashed the way root is.
Well I think it took me longer than 2 minutes, but still, I'd rather just flash it anyway. lol