I think the standard view is that this is exploitative, and I doubt you would find many students opting in.
The closest analogous scenario: there are pretty strict ethical rules against e.g. professors offering extra help to students in exchange for labor. Doing so would probably be grounds for inquiry and possible dismissal, even from a tenure position. I realize it's not exactly the same scenario, but it's probably as close as you can get where there are codified rules.
This seems to be exactly the case in psychology. Undergraduate students often assist with experiments in return for research experience on their resumes. Depending on the degree to which they were involved in a project, they may be thanked in a paper, but not listed as a coauthor.
Research is significantly different from private, for-profit business.
And those studies are always IRB-approved. The IRB takes into account the conflict of interest, and will sometimes protest if you don't pay the student subjects (e.g. if the study involves a significant time commitment).
I'm not talking about students who participate in experiments as subjects. The students who are research assistants are sometimes unpaid, and might not receive course credit for RA work, but contribute code to projects for research experience. It's relevant to working for a private, for-profit business in the sense that the alternative is often doing an internship for a private company.
The IRB only monitors study participants, not research assistant work.
> It's relevant to working for a private, for-profit business in the sense that the alternative is often doing an internship for a private company.
I still think there's a pretty significant ethical difference between not-for-profit research and a for-profit business. Even without the student-teacher relationship, unpaid internships in CS are pretty ethically dubious and uncommon.
The closest analogous scenario: there are pretty strict ethical rules against e.g. professors offering extra help to students in exchange for labor. Doing so would probably be grounds for inquiry and possible dismissal, even from a tenure position. I realize it's not exactly the same scenario, but it's probably as close as you can get where there are codified rules.