"So if Ziane has a connection to the Charmantaines case, such that he will give Malik info about the Oliver Hughes case, do we think that he was corrupt in that case also?
Taking money to make stuff disappear?"
Possibly, but it's not the only option (everything has more than one possibility, doesn't it?)
We don't know what the Charmantaines case involved or where it took place (France, UK, North Africa?) We do not know whether Ziane was a policeman when it happened.
My pet theory FWIW is that he was a policeman, in N Africa, and (a bit like Tony) beat someone badly. possibly causing an investigation to fail. He managed to suppress whatever it was (a bit like Tony and his FIL) and join the French police. Malik knows about all that, and can threaten his livelihood in France. (There may or may not be bigger secrets too),
He got really angry when he thought Baptiste was too gentle with Vincent at the first round of questioning (even grappling with him) and that is what provoked him to deliver the first batch of info to Malik. After which, he was utterly ensnared.