1) JAL is not BA.
2) I have never read reports on JAL IDG on flyertalk.
3) I have heard of JAL IDB-ing, however, outside of FT world.
4) I havent covered the japanese bloggers, nonetheless.
So, whilst i cannot confirm if JL overbooks F, I have always had the impression they prefer to IDB rather than IDG. I hope this helps with mitigating risks (Rather than giving you the answer you wanted/looked for)....