It's not cheating if it's in the game. I will say, however, that if the combination makes it so that people can't really play the game because you can dominate that hard, it's very close to cheating. As an example, let's take the Marathon, Lightweight, Commando class. If you really like running around and stabbing people with a knife, take Marathon, Lightweight and Ninja/SitRep instead. You can still have your fun without ruining the experiences of everyone else because you lunge across the map with an instant kill move after dropping down from the tallest building on the map like some demonic harpy on high, snatching away any hopes and dreams I may have for living more than ten seconds before immediately dashing off towards where I'm going to spawn at 88 miles per hour to create some backwards time shift loop that makes it so you're right behind me the second I'm alive!!!
...Sorry, what were we talking about again?
...Sorry, what were we talking about again?