Kzinti are Star Trek canon.
Niven himself wrote The Animated Series (TAS) episode ‘The Slaver Weapon’, adapted from his short story ‘The Soft Weapon.’
Niven sees Star Trek as a separate universe or timeline, but it shares the Kzin with his own Known Space universe.
In Lower Decks, there is an ensign who is Kzin in addition to Dr T’Ana being Caitian.
Also, it was Niven himself, writing on the official Star Trek website, who put forward the view that Caitians and Kzinti are cousins, with the Caitians having settled on their planet Cait, and adopting a more scientific and technologically oriented culture.
In TAS, Lt. M’Ress was the Caitian second communications officer.
There was a third species in TAS that some interpret as felinoid, but are more likely lemurians.
The ancient, advanced space-faring species the Vedala was introduced in the TAS episode’The Jihad’ written by Stephen Kandel, whose other episodes featured Harry Mudd.
Here are a few more images from TAS that show the breadth of sentient species that the show established