Is there a way to track which users have viewed a video within Stream?

If you have access to the Audit Logs, yes. Details here: https://docs.microsoft.com/en-us/stream/audit-logs . Just followed those instructions on our environment and they worked. Running report for all stream activities for a month took around 5 mins to display. So, it might go slow. Also, disable adblockers when in the security center. uBlock disables some of the submit/search buttons.