A couple of things:
1/. ViewNX2 is unable to convert to DNG!
2/. If you are sending to an external application via VNX2(eg. PS) .. it will almost certainly be TIFF.
3/. If you are converting from NEF to DNG(as you assume) and that is, saving in PS as a DNG .. it's not a true
raw file type!!
That is, you can save a jpg or a tiff image in your editor as an NEF .. but it's not a
raw nef, it's a psuedo NEF whereby it's a tiff/jpg with the ability to remember the edit steps.
Note that only a
raw file is a true
raw file!!
FWIW: I'd delete the DNG files once they've been edited and converted to a raster image(ie. tiff or jpg).
You can always reconvert any NEF to a DNG file type, but you can't convert a DNG file to a (true!)NEF.
Raw NEF files have intrinsic and unique properties about them.
Whether this is important to you is the unknown variable.
4/. I know 4 points isn't equal to a 'couple of points' but I'm sure you'll survive that encounter!