Yes, many hackers use Kali Linux but it is not only OS used by Hackers. There are also other Linux distributions such as BackBox, Parrot Security operating system, BlackArch, Bugtraq, Deft Linux (Digital Evidence & Forensics Toolkit), etc. are used by hackers.

Kali Linux is used by hackers because it is a free OS and has over 600 tools for penetration testing and security analytics. Kali follows an open-source model and all the code is available on Git and allowed for tweaking. Kali has multi-language support that allows users to operate in their native language. Kali Linux is completely customizable according to their comfort all the way down to the kernel.