Are 404s and 301s included in the render counter

Yes. While non-200 status pages are not cached - so they won't be recached automatically - search bots are still redirected to the Prerender service. Therefore Prerender needs to render the pages no matter the status it returns. As the usage depends on the number of renders, they count into the usage. 

Related articles: 

- How to Reduce the Number of Pages

- How to export a report of all 404s in the past XX days

- What you pay for - and what you don't

- Status Codes