Yes, that fitting would normally have to be unscrewed to get the rocker shafts off, but it can be reattached. When I said the captive ferrule fitting wasn't reusable, I meant getting it off without ruining it to put it on a new piece of tubing. Right now with the tube broken, you can remove the rocker shafts without messing with the fitting, as the tube will come off with the shaft oiler.
HERE's your fallback position, but I think the coupler will do the trick for you. That captive ferrule nut looks pristine - no one has rounded it off. Pull that piece off and check it out.
