The evidence is pretty clear it's incompetence.
I'd seriously doubt complicity; what did he gain from it? As far as I can see, nothing.
And it's not as if Kerik has a lot of pull with the mob. The guy's not even an associate, let alone a made man. He just took bribes from the Gambino family in exchange for helping one of their front companies get approval to do business in New Jersy. While that's bad, and corrupt, it hardly makes him a member of the organization.
I hardly see what Giulliani stands to gain from the Gambino family by appointing as police chief a man who once took bribes from them.
Apathy also strikes me as unlikely, given that he devoted his entire career as a prosecutor to bringing down the mob, and took big political (and possibly personal) risks as mayor to end some of their rackets.
No, the evidence is pretty strong it was lack of competence and possibly worse: nepotism. The fact is, Kerik was his close friend, so he didn't check him out like he should have. This reflects poorly on his judgement and leadership abilities, but it does not indicate any complicity with the mob or even apathy about their activities.
He he he...are you sure you belong here? You seem so logical...