Your martial artists will need 3 things; speed, flexibility and upper body strength.
The real issue with fighting in zero G is purchase. When Chuck Norris stands his ground against an attacker, he does exactly that; The purchase he gets from his legs on the ground means that when he strikes, the momentum he's building with his fist, foot, shoulder etc. is projected into the other person, not pushed back onto him. Most martial arts are based on the idea of strikes intended to catch your opponent wrong-footed or off guard, hitting them where they're weakest with all of your strength rooted so as to deliver maximum effect.
In space, you have to assume you won't be able to do that.
You might have the option of standing your ground wearing velcro shoes or something similar, but there won't be any spinning leaps et al. The reason is that once you're off the ground, it's all about momentum. Unlike on Earth, where you're going to land again, in this case you'll bounce off the roof, the opposite wall, your opponent, etc. once you get there, meaning that if your opponent weighs what you do, then there's a good chance that any momentum for strikes is going to be halved, with half going to your opponent as intended and the other half pushing you in another direction. This also means that your opponent isn't likely to be disabled because the energy will just push them back, especially if they are also off the walls or deck.
So; what you're going to have to focus on are holds. Not just any holds, but holds where ALL the strength comes from your muscles and don't rely on gravity assists. You can't use an opponent's 'weight' against them in space, you can only use the strength of your muscles and perhaps a wall (bearing in mind that there's nothing holding them to the ground or the wall which brings us back to your own strength).
You'll need speed to get your opponent into these holds, and avoid theirs. You'll need flexibility because in this environment, your legs aren't anchors so much grappling hooks and will be a major part of any hold you try out. And of course, upper body strength because you'll be holding someone against their own desire to get out, and without gravity assisted moves, the strongest muscles will tend to win.
I'd start by looking at something like Judo rather than Tai Kwondo because you want to start with the holds and then reverse engineer out the differences gravity makes to some of the holds and how you'd compensate. A good working knowledge of kinematics will certainly help you build up your own zero G variations to the holds and blocks you need to avoid being captured by your enemy. Speed is a factor, especially in terms of disabling people with guns, but that speed will be more along the lines of dexterity than single line of motion speed. In other words, how quickly can you wrap yourself around a gun laden hand? How quickly can you convince it to let go?
Training in this environment would use something similar to the wooden training poles that are used in many Asian martial arts, where you have a pole that you learn to wrap yourself around quickly and strongly. As for muscle strength, you'd find that any form of exercise will help with that but ideally there would be an additional focus on flexibility in that training. I don't know how Pilates would work in Zero G (I'm guessing it wouldn't because many of the moves are designed to take advantage of bodyweight) but it would be very useful in this regard because it wouldn't sacrifice flexibility for strength, especially if coupled with some form of Zero G yoga.
As a bonus suggestion, also take a look at Greco-Roman wrestling as many of the moves in that sport also require strong upper body strength and are tests of the ability of the participants to hold their opponent in check.