No, NiB-coated BCGs are fine. It's the military that does not allow it. Plus, a few of the CMP and NRA competitions don't allow it, as they require MIl-Spec coatings on the weapon for competitions. NiB coatings are actually a good thing if you get a good one as it cuts down on cleaning among other things.
I have them in my AR-10.
Look out for Teflon lubricants, though! Slipfires can and do happen if the tolerances are off enough, which tends to make range officers and any cops around want to inspect your guns!
Be sure to choose a BCG that’s a standard semiauto replacement from a reputable brand. Avoid any parts that are marketed as full auto conversions. That’s where you could find yourself in legal issues, not with the finish.