usbOTG can I invert the D+ and D- diff pair?
The device on the other end of the USB OTG connection can still be a regualar USB 2.0 device.  Therefore, if you swap the D+ and D- signals, you will effectively be swapping the lines in the cable.

But just to explain here explicitly why this doesn't work, see the blurbs below from the OTG specification.  Basically, devices use pull-up or pull-down resistors on specific lines to identify themselves at initial connection time.  D+ and D- are therefore not identical in functionality and cannot be swapped.


  5.1.6  Data Line Pull-down Resistance 
  
  When an A-device is idle or acting as Host, it shall activate pull-down resistors on both the D+ and D- lines. These resistors shall be within the range of 14.25 kΩ to 24.8 kΩ (RPD).  When an A-device is acting as a Peripheral, it shall disable the pull-down on the D+ line but shall not disable the pull-down on the D- line. The A-device is allowed to disable both pull-down resistors during the interval of a packet transmission, when acting as either Host or Peripheral.
  
  5.1.7 Data Line Pull-up Resistance 
  
  When operating as a Peripheral, the A-device shall enable a pull-up (as defined in the USB 2.0 specification) attached to the D+ line. It is allowed to disable the pull-up resistor during the interval of a packet transmission.