Over the years I have seen fittings made out of some really unusual or weird/strange stuff. Mostly on Khyber Pass tourist trade guns. Material like carved Jade, human rib bone, buffalo horn, parts from crashed WWII B17 bombers, braided Hemp etc. This is the first I've seen from rawhide though don't see why it wouldn't work though.
Back in 1985, I forged 2 bespoke trigger guards for a gentleman. One out of an old wrought iron RR spike and another from a draft horse shoe. They came out pretty nice. He wanted them to be recognizable for what they were made from.
Randy aka bpd303