Is there an IRB/ethics career path?
There are administration jobs involved in the ethics processes.  My university employs several "Ethics Officers" which facilitate the various ethics reviews.  Most of them do not have PhDs.  While these employees may not directly decide ethical issues, they do provide advice to researchers before the application is made which ensures the application is successful.  Knowledge of local laws is at least as important as knowledge of ethics; researchers usually need more help with the legal aspects than the ethical aspects of their ethics application.

If this sort of job appeals to you, then yes it exists, no you do not need to be a researcher to hold it, and I doubt you need to study philosophy.