I suppose you could use the scope if you wanted to. The tube on a scope is not all that strong. The design goal of a scope tube is to be only sufficiently strong to maintain it's integrity under normal working conditions. It is also designed to be as light as possible while serving the above purpose. It's not all that hard to ding, skew or torque a scope as it is made of lightweight aluminum. I guess I just feel a lot better using a free piece of scrap steel rather than a $500 scope as a ring aligment tool. I also use the steel bar to test the fit of the rings. I clamp the rings on then remove them and look for rub marks, either on the bar or on the rings.
The alignment rods in the picture would be used to ensure that "turn in" rings were parallel. I don't use "turn in" rings, there seems to be just too much opportunity to damage the scope. Or if no damage, at least skew the scope and cause additional optical and sighting problems. What I use for alignment is a 1" diameter steel bar about 12" in length.
Either method of course is better than just bolting the rings on and installing the scope.
Steve(AZ)