Dealers who like to see players lose:
1) "The company man", as some would say. This is the guy who, for whatever reason, wants his casino to make a bunch of money. He is most likely aiming to be a floor person and eventually a pit boss. He wants his table to have the biggest win of the night, so his superiors will see what a great employee he is, and he'll be promoted. He likely sucks at his job, tries to be friends with floor people, pit bossss, and management, but they all hate him anyway. He thinks he's the best dealer in the house and deserves to be promoted and would do a better job than anyone else above him This person is most likely retarded.
2) The dark/envious dealer. This person is just an a**hole and enjoys watching others lose. He thinks he should get paid more for his job, meaning he doesn't receive as much in tips as he thinks he should get. Thus, he enjoys watching players lose money because he views all players as not tipping enough. Even when someone is betting $500 a hand and tipping $25 a hand, if the player (somehow) comes up ahead a few thousand, he thinks the player should tip an extra 20% of his profits.
3) The player is an a**hole. In this case, the player is a complete idiot, typically always complaining about losing or not winning enough, complains about the slow cocktail waitresses, dealers aren't making payouts quickly enough, others messing with the flow of the cards in BJ or "the shooter been doing good then he changed his toss and sevened out, idiot", etc. This is the kind of player that anyone with a soul would like to see him lose, and rightfully so.
Few dealers are #1, because many hate their jobs. Also, floor people tend to make less money than dealers (AFAIK).
A huge number of dealers are #2. I'd say very few are truly appreciative of tips. Even though most will say thanks, you're a good person, etc., it can frequently be an attempt to pressure the non-tippers at the table into tipping.
Almost all are #3. There are a few odd balls who just love dealing and like players too much. Picture the manager dude at the restaurant who's too happy and out going in the movie Office Space
"should of played 'Go Fish' today ya peasant" -typoontrav