That shouldn’t be a problem.
This is a hybrid build (unlike mine which is pure caster) which is getting damage from both melee & DO (hence the Forgotten Knight sword. This means that all of the flat & % physical benefits Vengeance, however the only flat physical is coming from the sword. % Void would be more useful as it would buff Devouring Orb as well as Vengeance.
It’s not useless but it’s also not exactly a focus for the build (though the VK does get a lot of crit multi which is why he’s putting crit chance where he can).
No, because he’s not using any throwing skills (Shield Throw & Hammer Throw). You could switch in one of those for shield bash, but it would likely be worse since you’d have no flat throwing damage so it wouldn’t hit for much.
The gearing would be the same, how to spec the skill depends on what you want to use it for (I’m not really a fan of this skill though).