It's interesting to see this blog—that appears to have one foot in Chile and one in the US—looking at similar concerns. I especially appreciate the point where the author quotes from Scott-Jones' and Watt's
Ethnography in Social Science Practice:
‘To an extent, most field research requires a more flexible or situational approach to ethics, and it is naive of any researcher to assume that an overt role, combined with a signed informed consent forms, means that research is fully ethical‘ [Watt & Jones 2010:123]To me this means that the researcher must remain engaged, sensitive to the participants, and asking questions of the process throughout the process. There must be a willingness to "disobey" the approach if people are being harmed.
This is the lesson from Milgram and Tuskegee.
I would add that our ethical obligation to do no harm underlies all of the choices we make as designers, so I would think the research would be part of a continuum of activities in an ethical, integrated design process that would include every stage and every decision.