Is it safe to assign "Edit all events" to non-admin users?
It depends on the context and the definition of non-admin users. 

If, for example, your context is a small organisation with a small number of users I would say it is safe to do so. You could generally agree with each other that everybody is responsible for the events they have created which is usually the case anyway. 

But if you have hunderds of users who might edit other events the it might be something which is not really helpfull for your situation. Then you might think about other solutions for creating and managing events because manage own events is missing from the permission settings.