found this out the other night when i deleted my 80 dk and made a new one to lvl up with my brothers.
i gave my new DK at 55 the BOA axe with a higher lvl rune on it from my old dk and the new dk was able to benifit from the higher lvl rune even though he hadn't learned them yet
not very many cases where this would come in handy but it's helping me out a bit with tanking