I don't know what finishing process they use, but the mfs cases in 9mm i've handled looked nickle plated.Steel cases are probably not kinder to a firearm, but in general not a problem. When you think about how the case transitions from the magazine to the chamber, then out of the pistol, it's 99% sliding. The harder surface in the absence of a foreign abrasive is not liable to wear anything faster.
In guns like the SKS where the extactor must cam over the case rim, I could see the arguement, but practical use seems to suggest it ain't a problem.
The only case of steel cased ammo causing problems I know of was due to the lacquer coming off the cases and fouling the chambers of .223 rem rifles.