That grounding crap really gets complicated and how you do it seems to depend on where you live. Some places require you to tie neutral to ground and other places prohibit it, even though it's essentially the same thing in the end. And like you said it depends on if there's a ground at the house panel. I had to drive a rod into the ground and tie ground to it, but I think I had to connect neutral to ground in the panels in both shops, even though there's one at the house 100 feet away. I don't know why you would NOT want to do that.