A polish like the Meguiar's #3. Is a clearcoat porous enough to allow the oils of a polish to reach the paint? Any thoughts?

 

Why do you want the oils to reach the paint?

The oils are there to act as fillers to fill in swirls and imperfections. The imperfections in a clear coated paint will be in the clear coat and not in the base coat itself (some exceptions to that).

It'll work on a clear coated paint.