The answer to both questions is yes; i.e., a <section> can contain <article> elements, and an <article> can contain <section> elements.
For example, a personal dashboard page might contain a <section> for social network interactions as well as a <section> for the latest news articles, the latter of which could contain several <article> elements.
Conversely, an <article> might contain a <section> at the end for reader comments.
