And whatever the employer or fiduciary decides (or both decide), each might want its lawyer’s advice about:
whether and how to document the record of what information was considered and what analysis was done;
communicating the decision to meet whatever duties might apply;
even without or beyond a duty of communication, communicating to start the running of a statute-of-limitations period on a disappointed person’s claim.
Here is a related discussion with outside links that happened in 2018. There are discussions of to what degree an employer is obligated to accommodate religious beliefs under the law. There was a lot of disagreement you will see. But it might help you start the research and decision process I hope:
https://benefitslink.com/boards/index.php?/topic/62193-refusal-to-participate-in-dc-plan-maybe-religous-reasons/
I can't really comment on specific facts, but I will point out that IRC sec. 401(d) means what it says. I am unaware of any guidance or case that allows circumvention of requirement. Again, don't really know your facts.