You can aim train for every fps (or most at least) game and benefit a lot from it.
Even if its valo, maybe there is not much "active aim" in the game as vorkot said, but it is still there, and in some situations, especially duels, aim training can help u a lot.
There is a lot of pro players that benefit from aim training, PRX jinggg for example, EG Demon1, FNC Derke and others who are crazy players and can pop off with their aim and show you some crazy actions.
While there is also players who maybe dont aim train that much (or even none) and focus on their game sense (and probably in terms of aim, they benefit the most from learning and remembering all the angles on all the maps and using it to perfect their crosshair placement) and can show u some crazy strats and are aware of what is going on on the map - FNC Boaster (im not 100% sure about his aim training experience, he mightve done some) - no more examples needed for this one, this guy perfectly sums it up here.
Using aim trainers to warmup might be good, but from what ive seen, most (i would like to say every, but that might easily be wrong) pro, if uses aim trainers to warmup, after it - still always plays a dm/tdm to warmup in-game, and kinda transfer his aim trainer warmup to his in-game performance.
From playing dms/tdms you will get better, especially you might understand the guns better and other mechanics of the game (movement for example), but aim training - in terms of aim - will give u its not even close to playing dms benefits (if u approach it correctly, with learning proper techniques etc. - kinda whole other topic).
To sum it up - if u want your aim to get better - aim training will give u most benefits - but playing dms/tdms for some - might be enough - imo there is maybe a couple individuals in the world who without aim training might have a great aim that could outperform other players at their - top - level who aim train.