You could hook up a "nothing load" like a cell phone charger between the neutral and the high leg and it should work ok. But look at Steve-White's diagram. It tells most of the story. Any significant load hooked up that way is relying on the center tap of the opposite phases. It's vulnerable to fluctuations based on the balance of the loads on the "120v" sides of that center tapped winding. And it is loading those transformer windings in a way that the transformer is probably not rated for. It's just not a legitimate connection path.
Again, the neutral isn't a normal neutral like in 208 3Y or 120/240 single phase. It's sort of an ad-hoc neutral. I've understood that it was conceived as a way to provide a small amount of standard 120v circuits (for offices etc) in an otherwise industrial building where everything else runs off of 3 phase power. And in my shop, where almost everything I have is hooked to that 120/240 side, it's an out of place system. That said, I'm not really disappointed.
I'm sure Jim Brown's paper on grounding talks about how the ground/neutral in high leg systems does not represent a balance point wrt to currents and I wouldn't be surprised if it tends to exacerbate the "conduit transformer" effect in installations.
As always, I'm just an idiot on the internet. And I don't always remember things as correctly as I think I do.
