Let us assume I have a brick wall (rigid body) that I want to get smashed with an object (in a rigid body simulation). I want this object to be invisible in the render. Is that possible? How do I do that?
As of now, I see no reason why you couldn't add a Transparent BSDF shader to the smashy object.
Animation with transparent smashy thing:
My .blend file:
Also, as lemon points out, in the Properties panel > Object tab > Cycles Settings dropdown, you could uncheck the Camera checkbox. If you follow this course, though, you will have a disembodied shadow.
As Nathan Craddock adds, you can also turn off Render Visibility in the Outliner.