This line of GI discussion should probably be another thread, as IMO, it deserves it's own topic as a very important (maybe the most important of all) photorealistic feature that is currently missing from Poser rendering.
Anyway...

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Note that It isn't required that a surface be able to generate photons in order for there to be global illumination: Surface photon generation is a shader quality, GI is a property of the overall light model.
A simple standard test for CG light models is to set up a cornell box and observe the render.
Maybe someone with Python script experience will run a CB test or two with Poser's hidden GI feature?

The sphere is not generating photons, unless I'm mistaken. If the sphere were generating photons, then the ground could be a simple diffuse white and be affected by the sphere emmissions. The ground is pulling diffuse color from the sphere. Different concept altogether than GI.
The 'Gather Experiment' here reminds me of Bryce's True Ambience, with the addition of surface shaders. It definetly adds photorealistic qualities to renders; but isn't GI, and it's computationally expensive.
TA (NOT T&A) accounts for specular reflectance also.
Does the gather node pull in specular responses of a nearby surface?
Thats another piece of eye candy that adds realism to renders.
Take it for granted that it would probably increase render times to do so.

Friends don't let friends use booleans.