I'll just copy what I said here
about Luffy and Dragon:
After the initial shock, Luffy is very disinterested, not caring about Dragon as long as there are others more important. I said this in the Luffy vs. Dragon
thread as well I think, Luffy will be very disinterested in the whole Revolutionary business, and I can imagine Dragon will not like that much eventually. Maybe at first he will be like "haha Luffy, you really are as carefree as I expected.", but with more and more denials / disinterest from Luffy, Dragon might get a bit pissed: "Luffy, you can't just ignore what I've been telling you. You must join my side and fight the WG!!" But we all know Luffy will only beat the bad guys because he himself thinks they are bad, not because someone (even his dad) will tell him.
I'm not sure if that is enough for an actual fight, probably not, but I would still love to see one.