If we are to believe the elven myths, then there isn't a whole lot separating mortals from et'ada other than their tie to nirn. A mortal in a daedric realm, or rather one who calls the daedric realm home, could possibly be exempt from the dreamsleeve. Just a thought.
Indeed, I also tend to think this way. It's all about the binding and purpose. Time and time again, it's irrelevant of time to be timey
In other words, the Dragon does exist in all realms, but only because the realms want him to be. As was said in one of the creation myths, when Akatosh formed, it became easier for the others to express themselves.
So there's linearity in the other realms (otherwise it wouldn't even be playable in there), but not aging (unless I guess the prince would want it to be).