It is not, we have agents all the time try to board without even know where the pilot(s) are. They'll even resort to lying, I had one during a snow storm tell me the pilot was in the parking lot heading toward the gate. Called crew tracking, who found he was 2 hours out. Some agents don't want to deal with passengers, so they try to pass it off on the FAs who won't get paid until the pilot(s) show up and the door is closed.