I got a reply to your question from NX Nastran development. I posed the question by asking if PCOMPS uses a smeared approach like that which is done with PCOMP as they are converted to PSHELL representations and multiple materials for membrane, bending, coupling, and shear. I also asked if PCOMPS internally converts the solid element into a single solid element for each ply. Here's the answer.
Each layer is NOT converted to its own solid element and it does not use a smearing approach.
In the ply stack up direction the element matrices are integrated layer by layer. You do end up with a lot of integration points through the thickness and it depends on the number of layers in the element. However, the element interpolation functions are not changed by the number of layers. For example if you have a 20 node hex element you still have only a parabolic variation of displacement in the element regardless of the number of layers. If you have only a single layer you end up with an element that behaves like a normal solid element made of a single material.