It's a valid form of protest, and can be quite effective in certain situations.
In this case, however, it seems unnecessarily divisive. I'm sure the 1% don't give a damn about flag burning, but it's clear that a fair proportion of the 99% do. And you can bet that the former will use such instances to try and convince the latter that these protests are just an extension of the culture wars, thus helping to keep the greater mass of people conveniently divided on partisan lines.
Let me put it this way: if you were greedy and selfish and making stacks of money off our current economic arrangements, would you be worried or pleased by an outbreak of flag-burning amongst the Occupy protesters? Personally, I'd be laughing all the way to the bank.