It's real, but the conditions have to be just right for it to work and the results are uneven (i.e. even with the right conditions, it may fizzle, not 'Uneven' in the sense of accidentally creating a 500-year flood).
Basically in order to form raindrops, it helps immensely if there is some airborne particulate matter on which the vapor can condense. We've all seen long dry spells where there are massive piles of cumulus clouds that get darker all afternoon and are shot through with heat lightning, but nothing falls to the ground. The idea of seeding is to push this 'Almost' situation past the tipping point and trigger real rain to break the drought. It is basically a primitive method to try to nudge something that is on the verge of happening over the edge.
Assuming you are talking about technologies other than the VRWC Hurritron Mk V, we do not have anything remotely close to a technology that can form the cyclonic wind systems off West Africa that become our hurricanes, nor to make them either bigger or smaller as they head our way. It is basically pointless to seed the clouds of a hurricane offshore as they approach since the system will just pick up water to replace any load it drops before it gets to land anyway, and doing so would probably just add to the storm surge even if it did work.
