If they're "do(ing) their jobs," then by definition they're adding value to the firm. Unless, of course, management has failed its job and "their jobs" aren't corerct or shouldn't exist.
In my experience, most people add no value or at least distinct value to a company. They are fungible -- as interchangeable as a can of tuna. They have fostered an expertise that falls within certain parameters and their jobs are designed to utilize that expertise. But they don't help grow the business.
Perhaps I used the phrase "add value" incorrectly. What I meant to say was add value beyond their job description. Every successful person I ever met has done this.