They may have been trying to pry the rotor from the back side, and bent the dust shield in the process. It doesn't take much.
Rust isn't an issue on that one, but where it is, the dust shields rust to the point where they crumble off in your hand. A lot of us just peel off the surround, and call it a day (I did), rather than replace them.
As long as you're sure the rotor / axle spins true, no noise from the carrier, etc., I wouldn't let the dust shield stop me, if the deal was good. If you want to do preventative maintenance, replace the axle seals (they leak; I have to do mine), and in the process of doing that, you'll unbolt the backing plate of the dust shield (so if you want to replace them at the same time, that would be the time to do it). PS: Make sure the pinion on the axle isn't shot - see if the yoke (where the driveshaft connects to) turns freely more than about 1/4" by hand - if it does, you'll likely need to replace the pinion bearings (PITA job)
Finally, the G80 locker is plentiful in these axles, so you haven't found 'gold'. If it's marginal, walk away -- there are plenty of others out there. And, of course, if you have 4WD, the new axle has to match your existing gear (or you'll need to disconnect your front driveshaft).