At the moment, compositing is only supported where you wish to simply render your final still, or animation. Crowdrender in this use case works fine, apart from the limitation described here of course! You can setup your compositing nodes, turn on crowdrender, render the frames you want and they will appear in blender composited for you, provided you have the post-processor option for composting enabled.
What we mean by full support is where frames rendered using our system can be then run through the compositor just as you normally would and you can tweak the final result in the node editor. Frames are rendered on other machines, but not compositied in this case. They are made available to the compositor for you to tweak.
This doesn't happen with crowdrender right now due to a bug or perhaps design limitation in blender (hoping I don't get shot down on that one) which is documented here.
The problem is that blender in its current build will not allow a multilayer exr file to be loaded as a render result. Because of this, we use a single OpenEXR file to load the pixel data into blender. But this single OpenEXR format only supports one pass which is the combined pass. You will not be able to use separate passes in the compositor in this way.
This feature is a fix for this problem, so why is it not in the bugs section? Well, the problem really isn't in our code. Blender can produce an OpenEXR multi file that you can load into the compositor as an image, and you can use the multiple passes just as you would a render result ( a non-crowdrender one!). However, that same file cannot be loaded as a render result, it will fail to load.
So we are building an extra component to our software (which is why we think of this a feature not a bug with our code) to allow us to combine tiles from multiple machines and still provide a way to work with them in the compositor.