That is hard to say from just this description. However, what I can say is that there are multiple versions of DNG support in Apple’s decoder (at least two, and I think perhaps three). Older DNG files will be locked to an older version of the decode, which is worse than the current one.
One way to tell is to look at the Nitro’s RAW adjustment to see what sliders are present. If it’s an older DNG then you may only see a Gamut Mapping checkbox. For newer decode versions, there will noise reduction and other sliders.
If you have an image with the older decode, one simple thing you can do is to upgrade the DNG version. You can do that in DNG Converter – point it at your old DNGs and make sure to set the latest decode version (of course, do this on a copy of your older DNG). Then open it in Nitro and see how it looks and what sliders are present.