Hello !!
I would like to know if it is possible to do an unlit material using the play canvas stock shaders.
For example, if I set the environment like that. Is playcanvas still processing this Pass?
Thanks ! 
If you apply skybox in scene it will affect all StandardMaterials (PBR). And light will do as well.
What you can do, is instead of applying skybox, remove it, and put cubemap on each material you want to be affected.
Then if you want light not to affect geometry as well you can change mask property on light and meshInstances. mask is bitmask value, that has first three bits reserved (dynamic, baking, lightmapped), but the rest of bits are free to be used.
Light have mask as well. Changing those bits will allow you to set which light affects which bit in mask, essentially making light groups.
Bear in mind, this will lead to shader recompilations, which might be slow.
There is BasicMaterial as well, but there is no at the moment way to create them from editor, only by code. They do not have IBL and no light affects them.
Thanks for your answer! 
It would be a nice feature to add the ability to enable and disable parts of a material.