Since the markets are disconnected by the onshore/offshore RMB barrier, it should be completely unimportant to the free market price.
And it is a fact that all the markets are well-connected so that the prices are closely matched, except briefly when the price is swinging too fast, and with adjustment factors presumably due to fees or other reasons I beieve that it is arbitrage, in fact, that eliminated the "free fall" crashes that used to be common months ago, and has turned them into slower "viscous" falls.
The unity of all the markets became notable when MtGOX severed both the money and the bitcoin channels with the rest of the world. That is the sort of divergence we should see if China and the West were really disconnected.
I agree with you entirely, in fact. My "should" was "should, in theory, according to the stated policies of the PRC government." If their stated policies are not effective, I wonder how much impact their banking directives will have.