Never Dull contains "petroleum distillates" on a cotton wadding. Therefore aside from whatever potentially minor abrading effect the cotton wadding may have, I would not consider it an abrasive.
Nor do I feel the cotton wadding is substantially abrasive. I think the biggest potential for problem is rust. If you rub the cotton over rust certainly some of it will be picked up and become embedded in the cotton fibers. Now it has become an abrasive which will damage the surface of whatever you are trying to clean up.
As to Grey's comment, I wouldn't be surprised if never dull were to alter the effects of the nugui.
I have used never dull for years on motorcycle parts, guns, knife blades, etc. It does remove tarnish/oxidation quite well, but I find if the stain is really embedded into the steel it may minimize/stabilize it but will not remove it.
Please note: I don't use it on my swords. If you choose to do so, do it at your own risk.