I've not tried to make a nut or saddle from antler yet, but I have used both bone and antler in decorative inlay work for another project.... of the two I think antler is a bit harder than cow femur, which makes sense as it it used defensively during rut and has to be tough enough to withstand severe impact and torque without breaking.
Both seem to work well using tools designed for cutting metal, such as jewlers saws and pattern files. Finishing with silicon carbide abrasives and polishing like if it was soft stone or metal. I'd really like to see if it could be done with something like Agate or Obsidian, but I'm thinking that they might be prone to chipping and making sharp surfaces that might cause string failure.
Might be fun to give it a try though.... perhaps when I've fully retired and have waaayyy too much free time on my hands!?!