So, these, have been fairly useful. They don't seem to really work that well for chambered guns, but they do work well for unloaded ones.
I will be having a local CNC plastic shop make a new shelf for my gun safe, which has grooves milled in it, for the hangers to sit in, so that the top of the shelf will still be level.
It, probably, doesn't really matter - I don't think they could scratch any guns, and it would actually be fairly hard to knock them off the shelf, but I would feel better.