All of the Germanic Wal- names on this site contain the element wald
, meaning "rule", so I'd say that's where it comes from. I agree with you over hraban
. So it'd be "raven ruler" or something like that.
The Walhalla (Valhalla) translation seems unlikely - if I'm not mistaken, Valhalla is a Norse myth so the wal/val part would be from Norse rather than Old German
, and while mix-n-match-linguistics (:-D) names aren't unknown it's probably more likely that the two parts came from the same source.