Zulu has been putting on blatantly fake fights forever; check out this farce:
Or this grotesque imitation of a fight (I especially like the "takedown" at 3:39 and the fact that both guys do a good job at avoiding hits to the opponent's head during the entire thing):
In no way, shape or form has Zulu ever shown impressive skills in an actual fight; and I've seen at least 15 of his "performances" over the years.
The black skin thing is just a tragically romantic story built around Zulu and certainly didnt stop legit dark skinned Brazilians like Waldemar Santana from regularly fucking up fan favorites in real fights, including plenty of white ones.
Concerning Pereira I have, to put it mildly, serious doubts about the legitimacy of someone who claims to have never been defeated in >300 - real - fights (a record that is disputed by Ivan Gomes himself, who claims a victory over Pereira in a 1h55min fight in 1968...). It is proven (and uncontested) that he beat Carlson in a legitimate Vale Tudo fight though.
Kimura himself was a travelling "professional wrestler" in Europe and America who stated in an interview that he was extremely surprised that a can like Helio Gracie wanted to fight him for real, he had been under the impression that the fight was going to be fake.
So yeah, all I can say is that undeniable photographic, video and first hand verbal accounts testify to a lot of fake fighting going on back in the day, mixed in with actual athletic competitions.
Edit: Ivan Gomes was also involved in a lot of "pro wrestling" fights that didnt even pretend to be anything but pro wrestling. This site lists his "professional" wrestling performances for Antonio Inoki's prganization:
https://www.cagematch.net/?id=1&nr=80140&page=3
https://www.cagematch.net//?id=2&nr=4756&page=4