I make my living from blogging, so there's no reason you couldn't use it to pay for a wedding. I'm sure if you do a search, you'll find there are other people who have done the same thing.
If you're going to do it, though, you should start sooner than later. Every minute counts when it comes to getting the traffic that will attract sponsors. But you should be aware that the online wedding space is quite crowded. So if you don't have a plan to get traffic relatively quickly, you might want to put your efforts elsewhere. That's not the case if you're not concerned with getting all the money by the time of the wedding though. If you look at the blog as a long-term income source and you're capable of doing all the necessary work, then you have just as much chance as anyone to succeed.
Best of luck. :-)