I think rolling is important for a horse, and if the horse is blanketed 24/7, they should get a chance to roll without a blanket. I much prefer to let the horse roll in turnout, with no lead rope, since I do worry about the rope getting tangled in their legs. You can avoid this, of course, if you take care to hold it up and away. If there is no other choice, or we have come in to the arena do ground work, I will let maresy roll on the lead line.
As far as rolling in the riding arena or when other riders are presents, be guided by whatever the going practice is at your facility, but also be considerate so you don’t become the problem that makes them ban rolling in the arena! I understand all the arguments against it, but if it’s allowed where you are, then not your problem.
As far as rolling without permission, you should start a routine where you give a signal for the horse to roll. Maybe involving standing back, with a voice cue. And then mix it up. Come in some days with a dressage whip and tap tap tap keep him marching smartly in-hand for 5 or 10 minutes before you stand back, let the rope slack, and say “OK, roll!” Don’t let it be a routine of enter the ring, drop and roll, before you can even get him out of the way of everyone else. And if you longe, be prepared to back up the “don’t roll yet!” command.
As far as buck and blot when he gets up, if you know he does this, be prepared. If you know he doesn’t, then it’s a lot safer to let him roll in company.