Khameleon appears in N64 MKT and has a mention in a few of the MKD bio videos, and maybe Reptile's MKDA konquest I can't remember, so she is canon.

Chameleon, of PSX MKT fame, had a minimal story when you chose the 2nd of Shao Kahn's treasures after beating the game:



I like to think he is canon, since I like that mini story. No mention of him since MKT though.

Sareena is in MKM/SZ, the more prominent of the female assassins. She is also in MK:TE and MKA - defintely a legit character.

Now for Meat, I never considered him a real character, more of an alternate outfit. However, he had a lifebar and is in MKD's konquest, so maybe yes maybe no.

Out of all of them, only Sareena is in MKA for sure. And since this has now been answered, I'll close it up.