The Zulu Gestapo is a phrase that the Zulu Nation uses to describe themselves. It was first recorded on Afrika Bambaataa's song Zulu War Chant released in 1992. The phrase itself probably dates back to the early days of the Zulu Nation, in the early 80's.
Although many members of the Zulu Nation were graffiti writers who are well known for their secrecy, it seems odd that the Zulu Nation, an organization devoted to "Peace, Unity, Love and Having Fun" should compare themselves to a secret police force that is infamous for torture, intimidation, brutality and of course, racism. Maybe this should just be written down as another example of hip hop turning bad words into good words (or, as Run-DMC once said not bad meaning bad but bad meaning good). Or it could be seen of an example of very bad taste.
In any case, as far as I know, although they are involved in any number of activities, the Zulu Nation do not do any organized intelligence or security work.
I had once thought that Black Star coined this term on their song Definition in the verse:
Strivin for perfection ever since I was a snot-nosed
COLOSSAL, true original b-boy apostle
Standin on the rooftop with the, Zulu gestapo
But this was only a reference to an already invented phrase.
I originally wrote this in 2001, and since then I have read, in Don't Stop Won't Stop, that "Zulu Gestapo" was actually meant to contrast two different subcultures present in New York City in the mid-70s, the older, rougher gangs who had an obsession with nazi imagery; and the Zulu Nation, which was a much different subculture. The truth of the expression's origin may be lost to cultural history.