I can only speak from and engineers view but my hope is that I have a good enough relationship with my manager that we can have an open dialogue. You should also have pretty wide berth in what you can say, even if the complaints or comments are unjustified, sometimes people need to vent.
If I was scared to vent to my manager I would be looking for a new job.
If I was scared to vent to my manager I would be looking for a new job.