I might be missing something again, but if someone set's a 600 permission, doen't that mean only the user himself can see the file? I don't understand why this is relevant, as if that's the case, noone else can see the file. The only issue is if the user who does the vac backup backs up his own contrib directory logged in as himself.
As for backing up stand alone directories and files, doesn't vac do that just fine?
Cheers!
Johnny