so unless the cloud has water (rain) droplets ... inside it you won't get a return.
You have oversimplified. A cloud is composed of water droplets, the difference is the size of the droplets. The boundary between a droplet being 'cloud' or 'rain' is not absolute and it is possible for a weather radar to detect cloud droplets - particularly in convective systems and over mountainous terrain. These will usually give only weak returns, however.
Yes it's a pedantic point but it is important: Saying that weather radar 'cannot' detect clouds is incorrect. Plain and simple.