If you haven't watched the video of Chuck Hurley's meeting with the Des Moines Register's editorial board, I encourage you to do so. I know it is long, but it is a great demonstration of where both sides are on this issue, the arguments being used, and the rebuttals being offered.
(An employee could claim that having such a person as mentioned above in the workplace was interfering with his performance.)
(So employers are not only responsible for themselves and their employees, but also their customers and suppliers?)
Sometimes. Iowa law provides that these protections do not apply to religious institutions with respect to any religion-based qualifications when such qualifications are related to a bona fide religious purpose. Where qualifications are not related to a bona fide religious purpose, churches are still subject to the law's provisions, e.g. a child care facility operated at a church or a church service open to the public.