This seems like a case where clear communication in both directions is desirable. You as a hiring manager should disclose if a particular OS is required, so the applicant can tell you if that's acceptable or not.
(Maybe you personally do this -- I'm really using a generic "you" in this comment.)
In any case, this is all pretty academic. When I've been applying for positions, a tour of the office is always involved when interviews happen, and I can see for myself what OS the devs are using (as well as other working conditions).
That's how I knew my current position would require me to use Windows, and I was able to take that into account when deciding whether or not to take the job.
If working the job requires a specific OS you should mention it right upfront in the interview, or better yet the job description. Why is it the candidates job to telepathically guess at what hard requirements might exist? You have a requirement, state it.