With all due respect, I don't know of any fashion/portrait photographers who can shoot an interior image to the standard of a specialist in interiors. Sure, it may look better then what the clients can do on his own, but the thought process is so different when it comes to shooting an interior then any other type of photography, as it is with any genre. Lighting a mood lit space can be very tricky, especially since the chances of it looking lit get so much greater. And does he have the right equipment? Fashion photographers tend to buy strobes, but if there is no sun to worry about, using strobes will be futile. Tungstens will be the way to go, specifically fresnel lighting. Does he have any?
And as far as I am concerned, photography is about painting with light, and a camera is nothing more (whether it be digital or film) than a device the records light. There ain't no Photoshop digital tricks that change this.
I know what I am good at shooting, and only shoot that. If I where to shoot a restaurant and the owner needed some food shots, I would not think twice about outsourcing that to a food photographer.
And as far as feelings are concerned, do you want your images to make you feel good when you look at them or do you want the prospects of your client to feel "I want to eat there" when they look at them? Which is more professional?