The reason would be similar goals, a common enemy, and a way to achieve military parity, if not superiority. I don't need to go into Hussein's reasons.
Just as the muslims want the west (and especially the US) out if muslim lands, China wants the US out of her sphere of influence. She cannot challenge us directly, but she can get in some licks through proxies. And she can undermine any US public support for "foriegn adventures" by making the US public "war-weary". In other words, anything that weakens the US only strengthens China's chances of eventually claiming all the islands and land she believes it is her destiny to rule.
As for the need to blackmail an American administration, they controlled Clinton--at least initially--with money. But how do you control a whole elected government and keep one party from exposing the other--especially if they are in competition? A biological threat just might do it. It might allow you to steal all the technology you need to catch up...
I agree that there is no proof at this point, but I am still going to keep the prospect in mind...
The Chinese are active on all fronts and in many ways, some more subtle than others, some in which it seems to me that we are willfully blind (Panama Canal).
North Korea is the creation and puppet of Beijing and there are a ton of dots just waiting to be connected between China, NK, Pakistan and Iraq.
Watch for the current administration to start making the connections public if and/or when NK tries to make diversionary moves on our Pacific flank.