Marketo is all about "Person" or Leads. I believe there is no filter/trigger to identify new companies created. You would need to leverage that reporting in SFDC.
Floyd is right, there is no possibility to query companies if there is not at least one contact in the database for them.
Once this is done, the company update date is not available either. If you want to search on this field, the simpler is to create a formula field copying this update field. This formula field will sync to Marketo and you will be able to use it in filters.
FWIW, you can use a webhook to alert on new companies pretty easily (well, "easily" once you're used to the webhook realm).
The unique company list can just be another form of counter, like counting event registrations, etc.