Great questions. I have just bought the bag and am looking at the cross bar, so I would love an answer also.
Sounds like you can provide the answers.
Thinking about it, the cross bar may not fit as the FT bars are tapered and the cross brace probably needs parallel tubing to clamp onto. It is possible to get braces to fit tapered bars, but I somehow doubt the Ducati accessory will fit. Hope I'm wrong though.
Has anyone fitted the accessory cross-brace to the FT bars? Traceyleep, can you attach the bag just to the bars, without any cross-brace? If this is possible them whether the cross-brace fits is a moot point.