Could undergraduate degree be revoked for minor noncompliance in human subjects research? With the understanding that universities define "minor compliance" in various ways, I'm curious about whether an undergraduate degree could/ever would be revoked for the use of interview data gathered prior to receiving formal IRB exemption.

In the particular case I'm interested in, interview subjects were current and former elected officials and other "elites" accustomed to speaking publicly about the questions raised during interviewing but nonetheless granted anonymity. The student didn't initially realize he needed exemption given the subjects' backgrounds, but he ultimately sought it from the IRB. His thesis adviser approved the exemption request and said he could still use the interview data already collected for his thesis, although this was contrary to the IRB's stated policy.

The exemption was only granted after the student submitted the assignment, but the student was still awarded his degree. Could the student face revocation of his degree or other repercussions if something like this resurfaced? My sense is that such an extreme outcome could only apply to PhD students, but I'm curious to hear what others might think.
(Not an IRB expert - but will hazard an answer since I don't think we have many resident IRB experts)

First, it sounds like this is for a class "assignment" and was not published. In this case, it seems unlikely that this would meet the definition of research as it pertains to such things. The IRB apparently agreed, since it issued an exemption request - this does not mean that it approved your procedure; rather, it means that for whatever reason, it agreed that it was not necessary to approve your procedure. Not sure if this is because what you did posed "minimal risk" or because it did not meet the definition of research. If it gave the latter reason, then your professor is correct, and you were fine to use the data.

Second, there is the issue of responsibility - if there had been an ethical lapse involving this, whose fault is it? Normally it would be the principal investigator of the grant that funded the research. Not sure what changes in a classroom situation -- but, I'm guessing it would be the instructor of record. As you are an undergraduate student (and therefore don't have a PhD), I don't see how you could be expected to perform research without supervision. Assuming you were honest and straightforward with your advisor, thus, I think he would be blamed for a failure to supervise, rather than you being blamed for misconduct. 

Finally, degree revocations are exceedingly rare, and almost always tied to evidence of serious misconduct (e.g., plagiarism) emerging after the degree was granted. Doing research without IRB approval does count as serious misconduct; however, you personally are not on the hook per the above points. Even if you were, the cognizant authority (i.e., course instructor) was already aware of the issue at the time and dealt with it internally rather than beginning expulsion procedures. So, it would make little sense for him to say "I know I gave a good grade, but I've been rethinking it, and want to revoke the degree." Normally, a new complaint would have to be raised to even open the question of whether a degree should be revoked. 

TL;DR: your degree will not be revoked.