Is it possible to integrate the RSVP Add-On with Active Campaign so that I can send E-Mails from there? If not: is it possible to export e-mail addresses of the attendees? And is there an integration with Zapier so that I can connect AC and EventOn using this way?
There is no direct compatibility with ActiveCampaign or Zapier.
You can download attendees (with emails) by going to Edit Event > RSVP > Download (CSV).