Hard to tell from that video but it resembles a fire worm and I would remove it. Bristle worms some say are harmless but my experience is they are not in some cases and this will be a debate for ages. Im giving you my experience and I unfortunately had issues with tridacna. I dont mind some here and there but too many can be problematic. Good thing about Bristle worms are that there quantity is usually dependent on much detritus you have and if you over feed you can end up with an infestation. I was guilty of that.
Now a fireworm is a bit different and I would not allow one to stay in my reef, ever.