I have a snake skin I put on a bow that is tanned as well. I don't think the issue is if it's tanned or not, it's the method in which it was tanned. If I remember right, certain tanning methods use glycerine, which doesn't bond with glue, or something like that. I tanned my snake skin years before I knew of snakeskin backing, otherwise I wouldn't have tanned it, but I know the method i used, and it didn't affect bonding.