I thought at the beginning, Jordan says he came from a family of both his parents being accountants, however later it appears that Jordan's Father is an ex-Cop and a PI?
Max Belfort "Mad Max" was an accountant. The person who tipped Jordan off about the FBI and told him about Brad being in jail because of Donnie was Bo Dietl who looks like Max. So no, Jordan's father was not an ex-cop or P.I. but Bo Dietl was.
They look VERY similar
Belfort's father Max, was to "Maintain order" in the chaos they had going at the firm. It was a free-for-all, with sex/drugs/money/testosterone going full steam. Think Sodom and Gomorrah, and Max was the cop trying to keep things from getting too far out of hand, more like a way to keep them connected to the rest of the world. Remember the scene where they discuss EJ entertainment? He had to try to keep everyone balanced out.