Hi, is there an existing module to integrate with Siemens' Autec Babylon access control system & Milestone Video? Before I start developing with the SDK. Thank you

I do not know, not for sure. If it does exist already there is a good chance you can find it here: https://www.milestonesys.com/community/marketplace/start-exploring/

Also, I would try to ask Siemens. It is optional for Siemens to advertise on the Milestone marketplace, so there is a chance that they made an integration even if it is not on Milestone marketplace.