HRWPC_RFC_OADP_GET_OBJECTS uses evaluation paths (input parameter OBJSEL) for selection (ie. uses the OADP config). Therefore, you need to make sure you are using a correct evaluation path that will look not only at "direct" employees but also the "indirects" (ie. past that first level down).
RH_GET_LEADER is a different function all together, so you are not exactly comparing "apples to apples" here. It will actually traverse/climb "up" until it finds the "chief" for an employee (very useful for example to find a manager's manager).
I wrote a series of blogs on OADP config also if you want more help on that end of things.