Wands only (I think it may even be a beta feature or something I had to specifically activate in developer settings). Here are some screenshots of the various front camera uses:

http://media.bestofmicro.com/P/6/571146/original/room-view-c... - This view is overlaid on the game when you doubletap the system button on the wand. Edit: It can also be overlaid automatically when you approach chaperone bounds, but it's incredibly distracting when set up that way.

http://cdn.makeuseof.com/wp-content/uploads/2016/04/mini-cam... - This view is available when in the "pause menu" when the front camera is enabled. It's a little weird, because the view is attached to the wand but the camera is attached to your head.

I haven't played with an xbox controller on my Vive yet, but yes you can activate it with the wands, you double press the lowest button.

This feature isn't enabled by default though, you have to turn it on in the SteamVR settings (it's easy to find).