Dealers have always maintained that they prefer players winning, because winners tip more. That, however, doesn't translate in the other direction - tipping more might not make you win more, because tips are shared.
I'm pretty sure Arnold Snyder says this in one of his books: he'd be wary of any dealer who intentionally altered the cut or any other unethical/illegal thing (such as showing you a bottom card) in your favor because they'd be likely to do the exact thing against you if you were to cross them (or they perceived you were crossing them).
I usually tip when I win big, but that's because halving my EV doesn't bother me. I count for fun, not for the money.