Unless someone asks and you volunteer the information, or is able to read the EXIF data of the image, I doubt anyone would be able to tell with 100% certainty that you used a D7100 just by looking at the image. It would just be plain dumb luck that someone guesses it.
I read the question as, Would there be a quality degredation of any kind using the FX lens on the DX body?. Of course, I could be wrong![]()
No, if anything, the full opposite. The DX camera would crop to only use the better central part of the FX lens.