Correct usage of schema.org for logo?

This should work because it still uses the logo and URL itemprops within the itemscope of "Organisation" which is ultimately the markup it is looking for.

<div itemscope itemtype="http://schema.org/Organization">
    <a itemprop="url" href="http://www.example.com/">
        <img itemprop="logo" src="http://www.example.com/logo.png">
    </a>
</div>

I'd expect this to work if you ran it through Google's rich snippet testing tool to confirm.

The logo can also be as SVG.