Has anyone had any luck getting a Steam Controller working with VO?

Erm no, but it should just work? It's just a fancy assed BT controller after all. A better question would be, "Has anyone had issues with a Steam Controller + VO" - it will work.

Incorrect. It is not a BT controller. It uses some other proprietary wireless technology.

Well, more specifically, my problem is this: whether I run VO normally or as an add-on game through Steam, the only functionality I can get from the controller is a vague humming and rumbling from the touch pads; nothing else.

I have to admit, I too assumed it was just a fancy customizeable controller, but it seems a little more complicated. Up until now I've been using a controller in my left hand and the mouse on the right. I may have to return to that for the time being...

Did you try the big picture mode in Steam yet? Click on that controller icon in the top right corner of the Steam window. From there, you will find ways to customize it.

Sure, I can customize it in big picture mode, but VO just won't recognize any controller input. Pressing the steam button on the controller also fails to bring up the usual shortcuts, instead just dumping me back into the big picture mode home.
Well, I'll look into it further.

1st. I would look at the config.ini file. You should see an entry for the unit in that file if it is recognised by VO. If you do find an entry for the unit, then you just need to figure out how the buttons and all else is mapped. It might help to post the name by witch VO recognises the unit, if it indeed does. Forum members could have the data you need with out knowing due to VO not recognizing the Steam Controller as such, but under another name.

config file shows a usb joystick, but I don't think it's the steam controller. VO itself can't see a controller of any kind when I scan for one.

But: whilst looking for the config file, I noticed that although VO has administrator privileges enabled, Steam does not. I ran Steam as a administrator, and lo and behold, the steam controller (and shortcut overlay) works (although only as a configureable keyboard and mouse; VO still can't see it as a controller).

Problem partially solved, I guess.
Thanks all.

My understanding is that the Steam controller out side of Steam or with out the use of Big Picture Mode defaults to a Keyboard/mouse configuration. Seems you are on the correct path here. VO is keyboard/mouse input compatible (many players use kb/m flight control). It is quite possible that you may be able threw the use of binds and aliases in game configure the Steam controller to work as you prefer for VO play.