Will a live USB for a Mac run on a chromebook or windows computer? I created a live Kali USB for my Chromebook which single boots ubuntu mate. I was wondering, if I made a live kali(or other linux distribution) for booting on a Mac, so using .img instead of .iso would the .img still work on my Chromebook? 

In simpler terms will a live USB for OSX still work on a Chromebook or windows.
No, the disk should still be able to boot.

There isn't actually a difference between the operating system in the .img and .iso. They're just different ways of storing the same information. 

Kali(or any other *nix) distro is an operating system, just as Windows and OS X are. Whether or not an operating system will run on a computer is solely dependent on the hardware, not the software already on the computer.