It doesn't really matter what opinion I have on this matter, fact remains: if you're 'flying the gimbal' you're not flying the craft at that moment. If you can't have LOS because you're painstakingly tracking an object with your sticks (on the second controller), while watching you're screen, you're breaking the rules. I know, with (a lot of) experience it can be almost perfectly safe, but:
You will not be ensured for any damage and completely liable for the consequences, if anything goes wrong. A hobby pilot may get away with it, but a professional operation requires a team with observer/spotter anyhow. So why not have a second person operate the gimbal.
You will not be ensured for any damage and completely liable for the consequences if anything goes wrong.