The only thing that would concern Customs in the U.S is if it is pre-ban or not and nothing more. Usually documentation means something with at least a notary stamp on it or papers from the Govt of the country it came from. I once saw a case where someone was importing a 12 inch piece of tusk and we accepted a photo of the guys father who legally killed the animal years ago taken at the time of the kill along with other family documents.
Honestly, if I had to bring a razor with ivory scales I'd just pack it up and if it is discovered I'd play dumb and say it's a razor I've had for many years and my dad had it before and I haven't a clue what the material is. Unless you get a real hardass you should be OK.