Yes, Noob is the older Sub-Zero. John Vogel confirmed it in Fight Night. Yes, Noob is the classic Sub-Zero from Mk1. When he died, his soul was reborn in the Netherealm as a wraith of his former self.
No, they aren't the same person. Monster was the Elder God's champion at the time, but Shujinko defeated him (destroyed him?). When he met Scorpion, Scorpion was made into the Elder God's Champion.
On a side note, Monster was actually supposed to be Scorpion's alternate costume, but they decided not to.
I guess Meat is a real character. I mean, everyone from every MK fighting game is in it (except for Khameleon and Chameleon). So, uh, yeah, he is a real character. I have my theory - this is a THEORY, not canon - he's a corpse that exists without a soul somehow.
Chameleon never got a storyline. He was just a filler hidden character that had all the powers of all the male ninjas. But if it COULD be taken into consideration, when you find him, it says he is one of "Shao Kahn's warriors."

Meat and Chameleon are every bit as much a real character as any other Reptile had no story until they decided to put him in MK2. Was he not a true character until MK2? No, he was always for real. Just like all of em, no matter how rediculous some people might think it is. I really look forward to seeing Meat, Kameleon, Chameleon, Mokap and Blaze again in the future given a revamped look and story. With enough effort, any character can be made to be great.
And while some my think Drahmin and Kang are good enough for zombie characters, I disagree. Meat was far more interesting, even without storyline behind him. He's a meaty skeleton zombie, heaps cooler.

As far as I know Meat has always been considered a real character. I'm not sure if he had an ending in MK 4 but it's likely that he is just a demon from the Netherrealm serving Shinnok. Being that he was the ruler at that time then it's very likely. Besides, Liu Kang's body exists in Deception without a soul. Why not Meat?
Khamleon had an ending in Trilogy so that makes him canon as much as anyone else. It states that he/she is a member of Reptile's extinct race and that he/she has been watching the other ninjas from the shadows.
Here is the exact text of his/her ending from Trilogy so you can read for yourself:
Khameleon's former race were known as raptors. They evolved millions of years ago on Earth into intelligent creatures but fled the realm when it was destroyed in a battle between the gods. They repopulated a new realm known as Zaterra only to be driven to extinction by Shao Kahn when they lost to Outworld in Mortal Kombat. With Shao Kahn near victory against Earth, Khameleon contacts Reptile and shares the truth about their race with him. This turns him against Kahn, allowing Khameleon to lead a sneak attack against the emperor. This last battle results in the end of Shao Kahn and unification of Earth, giving Reptile and Khameleon the chance to beget a new generation of raptors.

yeah i think that Meat may have a history,own moves,.. in the future. But for Chameleon i disagree..he ́s such a undefined character..

oh know i understood the Monster/Scorpion stuff.. but u guys dont think that ́ ́Monster ́ ́ is a stupid name?? Did Boon say anything about him? Or only time will tell us..?
and thankx for the answers

let me try to fill in some more gaps from those questions...
Meat was an alternate costume in MK4, for everybody. You played a certain mode and beat everyone... and then you were able to play as Meat. But say... if you picked scorp, he'd have all of scorp's moves.... or if you picked sub, he'd have all of sub's moves. So he was only an alternate costume, but I guess you could say he was a real character.
Chameleon was the male ninja from the PSX and PC versions of MKT. He did not have a storyline. In the N64 version of MKT... there was Khameleon... who was a female ninja and had all the female ninja moves. She did have a storyline. So theres two different characters... Chameleon and Khameleon. I could be wrong however on which was male and who was female.
Monster does sound like a dumb name... but he pretty much is Scorpion. He has scorpion's fighting styles.... might have his special moves also (I don't remember if he used any when I fought him). Actually... he "isn't" scorpion... but I should have said... he has everything that scorp has... just a different look.

I was always under the impression that Chameleon and Khameleon were the same character. One being male and the other being female was just a way for the consoles to be a little different from each other.
I feel that since Chameleon has the bio then she is canon. Her and Reptile recreate their species in her ending so that would have to indicated the female gender.

Monster was originally going to be Scorpion in a twisted time travel plot. but it was too freaking confusing so at the very last minute they changed it and gave Monster the first name that popped off the top of their computer nerd heads. As for Chameleon, he should be a zaterrian sent with Kamelion to help find Reptile. Meat SHOULD (more speculation) be a citizen of hell who joins Rayden, during mk4, in order to earn his mortality back. But, he is confronted with a thought, is what he doing rightousness or greed? Ka/Chameleon's power should be color changing goo that they throw at you and crawls on you for a while, then drips sideways off of you and back at them. from there, they form something out of it and whatever they make is random, it could be your fighting style, weapon, or projectile. Chameleon should have 10 scorp spears that he swings around for a weapon.

hmm im pretty sure khameleon and chameleon are different characters...(khameleon is female)a little while ago I visited a mortal kombat site, dunno which what where, but it became clear to me that they are really two different characters...but dont kill me if im wrong

Yes, chameleon is the male ninja, Khameleon is the female ninja with a storyline.
As for Meat, he is one of the few secret characters that pop to give you a huge amount of koins like Sonya and Motaro.