Raging makes someone fatigued. Fatigued is -2 to abilities.The ring negates that, thus removing the downside. It doesn't actually remove fatigue itself, so I could see table variation with the errata'ed ring.
Ah, I see where you're going with that. You believe that because the ring makes you immune to some of the effects of fatigue, that you shouldn't be able to use rage?
I don't agree, but I can see you're side.
My opinion is that they are separate things - you're not bound to be fatigued when you come out of rage. The issue there is fatigue in general - does the ring really make you immune to some of the effects of fatigue?
Note in case this still concerns you - There are ways to rage and not be fatigued (be a high enough level barbarian, have a certain ioun stone, have levels of oracle with a certain curse, etc.).