Final answer:
Disability income is the type of benefit that is usually not covered by a nonprofit health service plan, as it is not a direct medical or related service.
Step-by-step explanation:
The question is about the types of benefits that may not be typically covered by a nonprofit health service plan. Considering the types of coverage often included in such plans, which generally consist of medical care, hospital services, dental, vision, and sometimes prescription benefit services, it is disability income that stands out as an unlikely benefit to be covered by a nonprofit health service plan. This is because disability income insurance is a separate type of policy designed to provide income replacement when an individual is unable to work due to disability, which is not typically a direct medical care expense or related service.