I'm not sure why you're associating testosterone with SDO, as testosterone has not yet been convincingly shown to be correlated with SDO. In fact we have had this discussion here before: http://lesswrong.com/lw/84i/social_status_testosterone/

That discussion is about aggression. Why confuse aggression with dominance? They are so completely unrelated it is not even funny. Dominance (status-relevant concerns) is an in-group behavior, while aggression is typically directed towards the outgroup.

The link with dominance (again: not aggression) is so well-known that T is used a proxy for dominance-oriented interests (status relevant concerns) in stereotype threat studies: http://www.reducingstereotypethreat.org/bibliography_josephs_newman_brown_beer.html

SDO is obviously so much more about status-relevant concerns in-group than aggression towards the outgroup.

Note: SDO is a clearly shitty test and I have specifically mentioned it as a counter-example of how not to do psychology. The question sounds more like a laughable cardboard-cutout parody of a conservative person than something real people would use to describe their views: "It’s OK if some groups have more of a chance in life than others." the problem is obvious - it is the simply reverted form of an egalitarian credo, instead of actually trying to figure out how different people think. For this reason, SDO is pretty much useless, because the researcher just basically inverts what he believes and checks if people agree with the reversed form... so I meant it as a negative example, but so far as it has any utility at all, clearly it is something related to status-relevant concerns?

Why would self-identification make it 'useful'? Certainly few would self-identify as psychopaths (to give an example), even though we know that psychopathy most definitely exists and is quite a useful concept.

Bingo! Precisely for that reason. Because psychopathy is a disorder. Once it is turned into something people can identify with, it is probably no longer a disorder. That means charity / understanding was restored, and it is no longer medicalizing differing opinions. Ability to identify with is a measure of to what extent is it treated as a disorder or not.