Research thesis: supervisor is also a research participant?

[aridapricot]

I am examining a research thesis for which the candidate has conducted interviews and observations as part of their research. I have noticed that one of the research interviewees/participants is the thesis' supervisor (this is a field with an "industry" streak and so the interviews relate to the supervisor's practice there).
I haven't examined many interview-based theses, and so I wanted to ask, in your field, is this something that would raise red flags? There's no indication in the thesis that the student has reflected about a potential conflict of interest here - I imagine the research has obtained ethics approval but I don't know if this is an issue that has been specifically flagged up to the ethics committee.
The thesis sections that discuss the supervisor's practice are full of praise, and, from what I know of the supervisor, I don't doubt that the praise is deserved, but it just feels a bit odd and slightly over the top. Like, if I was doing a similar kind of research I would design my study so that I didn't have my supervisor as one of my participants.
Should I contact the candidate's research committee/graduate office to check that these issues went through the Ethics committee, or is this overreach?

hmm, does seem odd to me. we have strict anonymity for human participants in research.

is there a sensible internal examiner that you could check with? or chair of the thesis committee? they should know what the local rules are.

What conflict of interest are you concerned about? You are not examing the supervisor, only the student. Whilst the supervisor has an interest in the student passing, they have no influence over the thesis examination process. The only problem I can forsee is if you feel they have not critiqued or used the information garnered from the interview with the supervisor properly. So long as they are evaluating all the information properly there shouldn't be a problem.

I'm assuming from your description that this is a qualitative study. Therefore, I agree there's a potential for the existing relationship between the student and this particular interviewee to affect the interpretation and reporting of the study results.

As a PhD examiner, I'd be expecting to see (a) reporting of any pre-existing relationships or knowledge of the interviewees by the student; (b) reflection on how such relationships might have affected data analysis and interpretation, (c) consideration of what steps were taken or could have been taken to avoid undue influence on the results by a pre-existing relationship between interviewer and interviewee.

You can look at the COREQ statement (Consolidated criteria for reporting qualitative research) https://www.equator-network.org/reporting-guidelines/coreq/, particularly domains 1 and 2, and see to what extent the reporting of the study in the thesis chapter has considered these issues.

I have to say, with my PhD supervisor hat on, I wouldn't be comfortable being a student's research participant. However, I don't think it's an automatic issue with this thesis - the question is how well they've managed to do a rigorous study while including their supervisor as a research participant.

Thanks everyone for the answers, this is helpful!
@parietal the sector that the thesis is on is quite small and because of the nature of the study, certain information would need to be given about each participant that would make it easier to know who they are if you know what I mean.
@Aaron95 maybe conflict of interest is not the right word, and I meant for the supervisor rather than the student... I mean chances are you student is not going to be very comfortable being hypercritical of your answers in an interview.
@NeverEnoughCake2 I've now read a bit more and I would say that throughout there is a bit of a lack of critical approach towards interview results, which is a problem that needs addressed... this could be because of the supervisor-supervisee relationship, or more generally because the sector the thesis is about is perceived to be as endangered, under threat, etc. and so quite a lot of research refrains from asking difficult questions.