I spoke with Hootsuite today and here is their reply:
Regarding the integration with Marketo, this is currently on the road map but we have not date as to when this will be available. We had a beta. It's been put on hold, as the initial iteration was not up to the standards that people wanted.
We will be re-opening it at a later date, but want to do so with the right resources.
With the recent emphasis on security, we've prioritised items such as 2-step verification, as our current clients have asked for it in an urgent manner.
so basically there is no way to schedule social media posts via marketo