Is it dangerous to run sweep on live database with active users?
No. Sweep is just another process accessing the database. All other users can keep working without any problems. Sweep only cleans up the records that nobody is using, so there is no chance to lose some data or see some invalid data.
The only issue with sweep is that it consumes a lot of server's resoures, and if you have a large database it might hog the server until it completes. So, even there are no data integrity concerns, if performance is important, it's better to run sweep on off-hours, or periods of low user activity.