Quote - I'm guessing about the specifics of what you've described, but I'd say no. There's no node that let's you launch any old ray you'd like. The only nodes that launch new individual rays that you can read the value out of are the Reflect and Refract nodes. These are constrained to obey the standard rules of reality, so they aren't all that useful for special effects, like SSS or seeing through specific things at a specific, user-defined angle.

No, it doesn't launch a ray - it tests the type of ray for which the surface is currently being evaluated. So if it's a direct line of sight ray from a camera it will be true when Camera is the ray type, and you can use an If block to apply the desired value for a camera ray. Light I guess is for illumination, since light passing through seems to be transmission and there are a couple of other values. Not that it helps here, unortunately, just offering an explanation (in as far as I understand what it does).