I need to summarize some Pardot data in Salesforce e.g. I want a custom field that shows me per contact/prospect how many page views (or some other activity)that contact has made in the last x number of months. Is this feasible to do in Pardot and then simply sync the field across or will I have to call the Pardot api from Salesforce?
At this time, Pardot activity data is not synced to sales cloud through objects or field data. Only through a visual force element. So with this in mind the simple answer to your question is "no".
For documentation on adding the visual force to a lead or contact page layout, follow this link.