Hi Shannon,
I'm not positive about this, but from my experience, it does not. I tried installing the add-in (I have Windows 7 and Microsoft 2013, including Outlook). Once the Marketo add-in was installed, Outlook wouldn't even open on my computer. However, as soon as I uninstalled, everything went back to normal. Needless to say, I haven't tried it again!
I work for a managed I.T. services company, so you can imagine that we try to stay on top of technology and many of our marketing and sales staff are already onto Microsoft 2013, so I would love to see some 2013 support for this add-in!
-Emily