I tried connecting an iPad3 directly to the MiniBrute using a camera connection kit and a USB printer cable. The message I saw was something like 'the USB device requires too much power'. I didn't try using a USB to USB coupler with a printer cable and dock cable.
However, there may be another technical issue at hand. When you connect a midi interface via the dock connector, music software on the iPad will recognize it and use it. But when you attach a USB cable to the iPad via the camera connection kit, what is there to tell the iPad that it is attached to a midi device (the MiniBrute)?
In other words, if you attached a USB cable, the iPad's apps would have to encode midi data and stream it through the cable. I'm not aware of any apps that will do this... most look for a known midi interface and use the CoreMidi toolkit.
For what it is worth, when I plugged in an M-audio Uno USB midi interface via the camera connection kit, it worked fine with no power warnings/restrictions. And my sequencer app was able to see and use the interface, once I went into it's configuration settings. I only tested Little Midi Machine.