Well assuming the Hackathon is on a razor thin budget (which I grant you it may not be) might be able to support adding some equipment which can be tasked to other things when not hackathoning and can be installed/removed in a variety of venues. The WebCam/Pi/Disk system is about $100 (less if you use the Pi's camera module).
You absolutely could go out and buy a video surveillance system of course.
So that you can incorporate plausible deniability, selective disclosure, and secret-sharing based quorum. Do you really want to have created a system that gets subpoenaed for automated guilt-by-association when it turns out that one of the participants is being investigated for thoughtcrimes?
You absolutely could go out and buy a video surveillance system of course.