I think Huntsman has a good chance for a few reasons.
One, you can't really question the man on experience. Executive experience, foreign experience, etc. He's got it all. And with people pointing out Obama's lack of it previously, and how that has possibly affected his ability on the job, it could be a useful tool.
Two, he was extremely successful as a Governor of a decently conservative state. He won relection with more than 3/4ths of the vote. Job approval polls were always generally high for him, hitting above 90's and being in the 80's when he left office. His State was ranked as the best managed in the country and as a top 3 good place to do business.
Three, this is an election about jobs and fiscal responsability. Lets look at Huntsman on this. The CATO Institute ranked him as the best Governor on tax policy in the country during his tenure. He was tied for 5th in total with regards to fiscal issues in general. He simplified the tax code, reduced taxes, and his polices were considered "business friendly". His only fiscal ding was his spending but lest we attempt to label him a "moderate" during that lets compare him to Republican darling Governor of the past election, Sarah Palin.
Palin's state expenditures went up roughly 0.9 billion per year while Huntsmans went up 1.2 billion per year. However, when you look at GDP you see that Alaska went up roughly 1.5 billion per year under Palin while under Huntsman Utah's went up at a rate of 8.4 billion per year. By the time Palin left, government spending was 28% of GDP. Huntsman was a full 10% lower, sitting at 18% when he left. Even more than that, Utah's spending as a percent of GDP went DOWN under Huntsman from 20% the year before he came in where as Alaska's went UP under Palin where it was at 26% the year before she came in.
To try and declare him a "moderate" fiscally based on the increase in spending would be an uninformed declaration, and one that doesn't jive with many of those who would do so having been the ones praising Palin's conservative credentials in years past.
So he's strongly conservative fiscally when it comes to taxes and at worst an average conservative with regards to spending. His state was voted into the top three, and then later as the #1, place for business in this country. His states GDP went up nearly 8% every year, almost tripling the speed that the U.S.'s GDP improves. The man's got great credentials when it comes to fiscal responsability and jobs which is going to be the biggest issues right now.
Fourth, the area he's "moderate" in is with regards to social issues. While a large part of the base is unquestionably worried about social issues, they also tend to be worried about fiscal issues. In this election, the fiscal issues I believe will trump it. The Tea Party movement was not started becuase of Abortion. It wasn't started about Gay Marriage. It wasn't started about porn or sex ed or DADT. It was started because of taxes, spending, and expansion of government. In elections past I'd say a moderate social republican would have significant issues with the base regardless of how strong he is fiscally. In this election, with the atmosphere as it is, I believe the base can and would easily rally around this guys fiscal credentials because in that area...which is the most important to many in the base currently...he's significantly different than the other side.
However, the fiscal issues are important, but to a less fevered degree, to Independents. Enough so that I think someone to over the top on the social issues...such as Santorum...would turn them off. The fact is that yes, you must get your base but you ALSO must get independents. The combination of strong fiscal / moderate social I think can do that and can't be compared to McCain who was questionably moderate on all fronts.
Fifth...he can't be made out as some crazy extremist. The Democrats and Obama can't make this guy out to be some lunatic fringe crazy person because in doing so they damn themselves as Obama trusted him to be Ambassador to China. On the flip side, its very easy to state that when the President...ANY President...asks you to serve your country its the patriotic thing to do to serve. I think his ambassadorship during the Obama Administration is more likely to hurt Obama than Huntsman.
Sixth...for those on the right that want to bash him for being a moderate or not a true conservative, in part because of the ambassadorship, he's got some backup for his republican credentials. On top of his fiscal record I pointed out above you can look at his past experience. He's served, prominently at times, in all three of the previous Republican Administrations: Reagan, GHWB, and GWB. His ambassadorship under Obama wasn't new, but rather simply another one after he already served in such a role for GHWB.
Of all the candidates, the more I look at the situation and this guys record, I think Huntsman might have the most legitimate chance to win.