The problem with Hibbert is that, like Bynum, he wants to be a central part of the offense, and he starts to sulk if he doesn't get what he wants on that end. And if he couldn't find enough touches playing on an offense-starved team like the Pacers, well...he certainly won't enjoy himself as the 5th option here.
And to those who would argue that he won't hurt us too much on offense, don't let his All-Star tag fool you. Last season he shot 43.9% from the field, and averaged 13 points, 3.0 offensive boards, 1.4 assists, and 2.2 turnovers per 36 minutes. For comparison, good ole Henry Sims shot 47.4% from the field, and averaged 14.4 points, 4.3 offensive boards, 2.1 assists, and 1.7 turnovers per 36 minutes.
Finally, there's the issue that he's only effective defensively against certain teams. If the opposing center can hit jump shots (Bosh, Gasol, Horford, Jonas, Jefferson, and Antic all come to mind in the East), then Hibbert can't camp in the paint all day, and once he's out of the paint he's no longer a plus defender. This stands in contrast to defensive specialists like Asik who can be effective in any situation thanks to their tenacity, high motor and lateral mobility.
Maybe I would be willing to kick the tires on him if his contract were more reasonable, but 15M/year just seems absurd for a guy who's so mind bogglingly inconsistent.