You worked with Dauntless too? Did he ask you to delete all his "traces" in AC modding too..? (still salty about the way he left the ship)
And yes you can use all sorts of tileable effect in the metal_detail files. One of the stock Kunos skins for the Alfa GTA has a unique combination of metal detail and map files, resulting in a brushed metal look of the skin.
I was really sad to see Dauntless go TBH. After he left and I read that he didnt want you to use the stuff he had created for your 996 (I think?) I took it upon myself to remove my videos of his mods and stuff. Much less frustrating for me than yourself as I havent created anything really, just spent a whole lot of time doing precious little just researching, testing & trying to make skins... Dauntless and Henri are a lot better at that though, it was very much a learning process for me. I mostly just tried to find bugs and dig out articles that might be of interest etc.
Although i had a lot of hours poured into that stuff I did it for fun and was only there to help where I could, must of been a much bigger blow for yourself! I wonder if he would have reacted differently if Kunos had given a few weeks notice where people could still post in their threads. I really wish the LX8 got released and I could still use the XJ12C online