Семантика элемента header?
Найден пример в текущей спецификации HTML5, который косвенно указывает на возможность такой верстки:

<footer>
  <nav>
    <section>
    <h1>Articles</h1>
      <p><img src="somersaults.jpeg" alt=""> Go to the gym with
      our somersaults class! Our teacher Jim takes you through the paces
      in this two-part article. <a href="articles/somersaults/1">Part
      1</a> · <a href="articles/somersaults/1">Part 2</a></p>
      <p><img src="kindplus.jpeg"> Tired of walking on the edge of
      a clif<!-- sic -->? Our guest writer Lara shows you how to bumble
      your way through the bars. <a href="articles/kindplus/1">Read
      more...</a></p>
      <p><img src="crisps.jpeg"> The chips are down, now all
      that's left is a potato. What can you do with it? <a
      href="articles/crisps/1">Read more...</a></p>
    </section>
    <ul>
      <li> <a href="/about">About us...</a>
      <li> <a href="/feedback">Send feedback!</a>
      <li> <a href="/sitemap">Sitemap</a>
    </ul>
  </nav>
  <p><small>Copyright © 2015 The Snacker —
  <a href="/tos">Terms of Service</a></small></p>
</footer>

Тут речь идет об элементе footer; семантически, он имеет смысл, практически аналогичный элементу header.
Я думаю что так делать не стоит. «A general rule is that the section element is appropriate only if the element's contents would be listed explicitly in the document's outline.», — developers.whatwg.org/sections.html#the-section-element