Our goal in providing functions such as GT_curTime is to make software modlues that use these APIs platform independent. Depending on which platform you are building for, below GT_curTime there are corresponding OS calls (Linux for ARM, BIOS for DSP...).
The retun value for all implementations of GT_curTime is a UINT32 which represents microseconds.
Normally, we try to provide this API level details in the doxygen generated documents included within DVSDK; In this specific case, I agree that information on the what the return value represented (micro-seconds) was missing and we are taking steps to correct this.