If they are standard USB implementation, then perhaps that'll be the case. But neither A15 nor HA-2 is exactly fully USB compliance. According to Oppo, shorting Pin 4 and 5 stop HA-2 from drawing power from the microUSB port, which is probably how they have programed the XMOS USB controller to tell whether it is connected to a PC or an OTG Host. Here is the HA-2's OTG cable should look like, as confirmed by Oppo.
7/7/15 at 6:14am