Hi Alex,
I have tried several of the coating materials on this type surface with mixed results. With Alfa's with the cast camshafts, that becomes the NEXT problem. Cam surface is too soft. The DLC coating is applied to the follower (or whatever) after hardening, and provides a very slick surface. It does not cushion or reduce pressure on the cam lobe. I'm not sure, but I don't think DLC can be used on cast iron due to porosity. I looked into this once, but remember there was a problem.
However, the followers, correctly hardened and coated, would be better than uncoated, for any application.
Just my opinion.