Pulling while in cutscenes: I consider this bad etiquette. Is it allowed according to the TOS? Probably. Does that make it okay? No. It's like, it's legal for me to fart in a crowded elevator when I could have held it in, that doesn't mean I should do it. Playing a social game in a co-op PVE duty suggests you should be prepared for working as a group.
Complaining about early pulls: Getting angry is completely fine, so long as they aren't insulting or attacking. Saying "Hey, that is considered rude! I don't like that you did that at all!" is acceptable, it's like filing a complaint. You can be angry when you do it. Just don't make personal attacks and you can call them out as you need to. If you make a personal attack, that doesn't make the puller right, but it does make you abusive, and you should be able to get your point across without losing your own social skills.
I was in a dungeon where melee LB3'd early and then we had a lot of deaths afterwards. Someone complained and was abusive towards the melee for LB3'ing when we still had some way to go and now we couldn't use LB3 for the instant revive. I agreed that the LB3 was badly timed but I reported the abusive person, as did two others. You can complain, but being abusive is never okay.
I do think it would be very nice if the game implemented a system where, should someone who was new to the dungeon be in the duty, you were unable to engage with the enemy during the time that a cutscene is in effect. This means you couldn't even log out and come back in and engage (I know people do this at times) - the target would simply not be able to be attacked. If this could be done (and again, only to trigger when a new player bonus is in effect) then I think it'd save everyone a lot of wasted breath.