I would not install a lockring without it. I even take the very thin spacer (found on Shimano lockrings), remove it, and apply a little grease on both sides. Then I grease the threads all the way around.
Once you have to remove a lockring that's really stubborn you won't ask this question again. Shimano lockrings kind of "ratchet" when you tighten them down. They are not going to slip. If you torque them down to the spec etched right on the lockring - without greasing them - then, best luck getting them off if left on for any amount of time.