I've opted to leverage Marketo data in Tableau indirectly via the SFDC connector, but would love to pull Marketo data straight into Tableau if possible.
No native integration exists between Tableau and Marketo from what I've seen, so I imagine what needs to happen is to pull Marketo data via the API into a separate database, and then integrate that with Tableau. That sounds a bit janky, but I'd still be very interested to hear from anyone who has accomplished this--we're starting to use Tableau more and more for reporting purposes.