I don't think there's a difference between writing for a newspaper or magazine and doing a chapter in a book.
There are these boutique writers out there who think if they are not writing their novels sitting at a bistro with their laptops, then they're not real writers. That's ridiculous.
It is not unusual to send someone to conduct an interview you don't have time to conduct. It's what we do.
Most national correspondents will tell you they rely on stringers and researchers and interns and clerks and news assistants.
I have dictated stories from an airport after writing the story out in longhand on the plane that I got from phone interviews and then was applauded by editors for 'working magic.'