It sounds like a good time for your friend- if people continue to refuse vaccination, and the workload in the transition is survivable, there should be good advancement opportunities if a couple hundred+ people leave the company.
Also, NOT sharing the number could make people incorrectly estimate the risks of going into the office. Why would they not share the number?
Lastly, what mainstream religion is actually antivax for anything besides covid? Assuming this is the US, the majority of religious people in a typical business will be christian. The only religious groups in the US that have demonstrated a precedent of rejecting vaccinations are Christian Scientists, and the Dutch Reformed Church. Both of these are small groups and a tiny percentage of the mass of people who would be called christian. Therefore, just going off of average populations, the vast majority of those 300 exemption requests would be bogus.
PS: I doubt you will find many, if any, people on this forum who will have submitted a religious exemption request for this vaccine. This is a forum for a blog that while pro individual responsibility, is also explicitly environmentalist and pro community, to the point of advocating for higher taxes. This isn't a point of view that is shared with the majority of anti vaccination proponents.