No it's not. I as a lifelong Red Sox fan want to not only see them win, but want to actually like the players they have on top of that. If they had a winning team but a bunch of asshats, it detracts from the winning.
The best examples I have are these: Chris Nilan on the Bruins. Love the team, hated the guy. Made me sick to see him wear a Bruin's sweater, and I certainly did not cheer for that loser. And Wil Cordero on the Sox. Beats his pregnant wife up with a telephone because she interrupted him, gets suspended, comes back and hits a game winning HR, and the crowd cheered for him. Not me. The guy was a dirt bag, regardless of the win or any big hit he may have gotten.
So yeah, it does matter if the player is a likable guy or is going out of his way to make sure everyone knows he hates it here. If he hates it so much, opt out. Stop taking the money and go somewhere you will be happy playing for.