Early in my career, a salesperson described our accounting department as "the most important, least important people at the company." He meant that while no one thought of them as important as Sales, Product, or Engineering, the people handling your expense reports, signing off on your initiatives, or reviewing your complex, multi-year proposals have more power over your day-to-day life than most executives. They can make things happen fast or move them to the back of the queue, and nobody will ever question their priorities.
Samuel L. Jackson nailed it: "The feet you step on today are attached to the ass you kiss tomorrow." I've watched "ambitious" managers be jerks to freelancers, support staff, and the other people charged with "doing the work." Then they wonder why life is always so hard: their work gets de-prioritized, their problems never quite make it to the right desk, no one ever makes an exception for them.
Treat people the same when you need nothing from them.
Rather than searching for the uncredited people that keep the wheels turning, simplify your approach: treat everyone warmly, until they give you reason not to. And avoid the toxic people, with grace. Often, they are making their own bed with their behavior.