I haven't used it as a backing, but I tried to use it as the core in a bamboo backed curly maple bow once. I bet it had more frets in it than any bow you've ever seen. Dozens. I should have kept it just because of that... but I eventually burned it.
Yes, the curl is due to grain variations. These variations would be violated when flattened for a backing piece. When working, especially carving, curly maple gunstocks, sometimes the curl will crack or a small piece of the curl will even pop completely out.
I wouldn't waste my time and material using it as a backing piece.
If it looks nice enough, I'd use it in a glass bow under clear glass. That's what I save mine for.