You mean like having heatsink fins on the top of a waterblock? That worked back in the day of drilled passages, because the block had fairly poor conduction to the water, and more mass of copper conducting heat to the top of the block. It would be useless with modern waterblocks because there's not much copper bringing heat to the block top with channels and hosebarbs there.
If you mean for having aircooling on other components, well yes! Can't watercool everything, so it's still necessary to have good airflow in your case. The radiator fans take care of most of this, but if your gpu for example has aircooling, a duct to it would still help it. Just don't get too crazy with other air sources that will fight the airflow through the radiator...you don't want to hamper your airflow through that.