Insurance companies can include and/or exclude anything they want, subject to laws, some of which are at state levels. (Some states, such as Wisconsin, have state-mandated benefits that any policy written in that state must include).
Depending on whether the policy is fully insured, self funded, or fully funded, your employer also can decide what they want included and excluded.
Each policy is different in what and how they can include/exclude.
It is most frustrating sometimes trying to get straight answers and comprehensive information from the insurance company about some coverages.