Religious tolerance goes both ways. While it is true that Islam does NOT require or condone that behavior, he believes it does, ergo, it is his religious belief. That does not excuse his intolerant behavior of your wife, since she deserves the same respect he wishes to be accorded.

Rather, he seems to have an issue with women in authority, since he is doing the requirements of his job (i.e. answering questions) when it comes to other women.

Obviously, this is a dilemma for the HR department at the company, but if he were my direct employee, I would make it clear to him that his satisfactory performance of his job, and therefore continued employment, requires that he follow appropriate procedures including the chain of command and showing respect to his supervisors of any gender. Under US law, one only need to provide "reasonable accomodation" -- changing the management structure of the company to cater to one individual would not normally be considered a reasonable accomodation. The concept of reasonable accomodation, however, might require switching him to a department or shift where he reports to a man instead (if available). Which I think is plain silly, but there it is.

Oftimes, problems with employees like this can be solved if it's approached in an even-handed manner. I would suggest that your wife try not to get personally involved, but refer the problem directly to HR since it's a murky religious/gender issue, and legal issues may come up.