Like Xdashdriver pointed out, it is within his right to evaluate the applicant on any area listed within the ACS (as was the case in the PTS). I, too, am a commercial-instrument + instructor helicopter guy that got his commercial ASEL, AMEL, airplane instrument, and CFI/CFII/MEI all as add-ons. My checkrides have varied wildly as to what was covered in regards to what is listed out in the PTS/ACS.

My main advice to anyone adding a category or class to their certificate is to treat the checkride like an initial certification. The task table should be emphasized, but the wildcard tasks or academic questions can and more than likely will come up.