The fact that they are usually feeds of porn-stars is a dead giveaway that it can easily be run by someone else. On some forum about fake streams, there was someone giving someone else advice that you absolutely need footage of someone waving at the camera, typing, etc. Many porn stars have done streams exactly like this. There's been a fake one of Lexi Belle on SM for a while and she's cammed before (on SM and MFC mainly I believe).
Example, this is Lexi's actual streamate account:
https://streamate.com/cam/LexiBelle/
This is a fake account pretending to be her:
https://streamate.com/cam/LexiHotty
If SM were running pre-recorded shows, why wouldn't they just have something set up so it can be on her real account?
Anyway, as before, I highly doubt that SM is running these fake feeds, however I do think that they let a lot of people get away with running them.