I've only worked with one preloader long enough to be able to make assessments about his performance. I explained to him that I understood how hard his job was, told him I would never ask for perfection from him, just his best effort and communication when necessary. He wasn't the best preloader, but I know he went the extra mile to take care of me. I'd buy him breakfast every Friday.
To answer the question, I personally feel that I should tip the preloader when they deserve it and at the very least try to help the ones that need improvement. It's a hard job and a critical one. A little understanding, tolerance, appreciation, and incentive can go a long way to motivate someone to do better. I don't like being treated like
by my superiors who can't see the big picture, I sure as hell am not going to pass that on to the preloader.