A note of caution, though: in my experience, you can’t shield bash orc warriors off of high ground. I’ve tried it extensively and it never seems to work. I think they’re just too darned heavy to shove around. Young orcs and I think berserkers are a different story.
Orcs are immune to shield bash. If you select the skill and hover over or select the orc the game says that they are immune to shield bashing.
Not quite sure if it was only the warriors or also the other orcs.