Some of this seems to be slightly innacurate, so I'll add on what I know.
Jee Sin (more commonly Gee Sin Sim See) was not involved in Wing Chun in any way that I have heard of. He WAS involved in the creation of another popular martial art, Hung Gar. Hung Gar and Wing Chun don't really have that much in common though, Hung Gar emphasizes low stances and powerful strikes.
But that's not the point.
Also, Chi Sau is not a form, it's actually a concept/training device. It's key to the system and teaches sensitivity. You never break contact with your opponent, always touching forearms.
My Kung Fu teacher can literally close his eyes and block everything you throw at him, he has so much practice that he can tell if you throw a punch or a kick, with which limb, and where it's going.
Without Chi Sau (Chi Sao) training, Wing Chun would be a FAR less effective system than it is.
There is also a less-practised exercise called "Chi Gerk", which is much like Chi Sao only it invlovles the legs and you try repeatedly to kick each other in the nuts. It stings.