IPad – Stream iPad audio to other devices

You cannot directly interface with generic USB devices from a stock OS iPad unless you are a manufacturer in Apple's MFi (http://developer.apple.com/programs/mfi/) program. There appears to be a ton of paperwork involved to just apply. The external accessories API is of no help on stock OS devices, unless you are manufacturing your own custom MFi-compliant device.

Alternatives

• If your USB device can pretend to be a MIDI instrument or controller, you might be able to interface with it over USB by sending/receiving MIDI messages from the iPad.
• Another option is to use a small inexpensive board, such as a Raspberry Pi Zero W, and use it to programmatically transfer USB data via WiFi to an iOS device.

Unfortunately not. The VLC app was yanked from the app store some time ago due to some political issues within the developer base and conflicts with the app store policies. It hasn't been updated since then, and likely won't in the future. Also because it plays video in formats the iPad and Apple TV don't support, it's unlikely AirPlay support could be added anyway.

You might be able to use the iPad HDMI adapter to mirror the display on the TV, but I'm not sure how that performs with video going.

It's a bit outside the scope of AskDifferent, but there are several boxes similar in concept to the Apple TV that support a lot broader range of formats (much closer to VLC's level of support). I'm not aware of any that interface with an iPad, but most play from an attached hard drive or a network share. The WDTV Live and the Patriot Box Office are two popular ones, but there are many more.