At the moment as far as we know there are not benefits from using HTML5 markups such as header and footer. Using such markups just allows for better semantic markup.
Google, Bing and Yahoo have no problem reading header and footers within article tags, but you should only use the header and footer if it makes sense too and makes mark up easier. Consider Header, Footer exactly the same as DIV elements for grouping of multiple elements, if you do not have multiple elements then there is no need to group them. People debate this and your find mix debates but bottom line is, I consider the least amount of code to be better. But in terms of markup SEO value there is no difference in using or not using <footer>
or <header>
.
Not so useful HTML5
<article>
<header>
<h1>Title of Article</h1>
</header>
<div>
<p>I am the content of the article</p>
</div>
<footer>
<p>Author: Author Name Here</p>
</footer>
</article>
Useful HTML5
<article>
<header>
<h1>Title of Article</h1>
<dl>
<dt>Publish Date:</dt>
<dd>2013-01-25</dd>
<dt>Authors:</dt>
<dd><a href="#">Author Name</a></dd>
</dl>
</header>
<div>
<p>I am the content of the article</p>
</div>
<footer>
<dl>
<dt>Tags:</dt>
<dd><a href="#">Tag Word 1</a></dd>
<dd><a href="#">Tag Word 2</a></dd>
</dl>
<div>About the Author</div>
<nav>
<ul>
<li><a href="#">Link 1</a></li>
<li><a href="#">Link 2</a></li>
<li><a href="#">Link 3</a></li>
</ul>
</nav>
</footer>
</article>
So basically the more code you have to stick in footer and header the more useful it becomes as styling and markup becomes easier. I consider HTML5 much better for marking up using schema. Look at the example above and then look at example below but this time using schema and rich snippets.
HTML5 with Schema
<article itemscope itemtype="http://schema.org/Article">
<header>
<h1>Title of Article</h1>
<dl>
<dt>Publish Date:</dt>
<dd><time itemprop="datePublished">2013-01-25</time></dd>
<dt>Authors:</dt>
<dd><a rel="author" href="#">Author Name</a></dd>
</dl>
</header>
<div>
<p>I am the content of the article</p>
</div>
<footer>
<dl>
<dt>Tags:</dt>
<dd itemprop="keywords"><a href="#">Tag Word 1</a></dd>
<dd itemprop="keywords"><a href="#">Tag Word 2</a></dd>
</dl>
<div>About the Author</div>
<nav>
<ul>
<li><a href="#">Link 1</a></li>
<li><a href="#">Link 2</a></li>
<li><a href="#">Link 3</a></li>
</ul>
</nav>
</footer>
</article>