It is true that the evidence is not conclusive yet. But it was also stated by scientists quite some time ago that if we wait for conclusive proof of global warming, it will be too late to reverse the effects.
But as you say there are other ways to manipulate climate locally and without care, that may have knock-on affects in other areas. There again, those clouds they seeded may have dumped their precipitation into the Pacific Ocean and that wouldn't have made much difference one way or the other.