Wargaming EU has basically absolutely no policy regarding illegal mods.
They claim to care about it, by stating that each individual player has to judge whether or not a specific mod gives them an advantage towards other players.
And if a mod does that, then it can be considered illegal.
The thing is though, everyone judges differently. For some people, every mod gives you some sort of advantage. And for others, no mod seems to give them any advantages.
Thus, making this "policy" completely void in the overall picture.
That being said, the reload mods use really basic assumptions about the reload times.
They don't account for things that can influence a reload, such as crew-status, equipment and/or consumables.
Therefore, the mod is really only an estimation of the very basic reload and not 100% accurate at all (it may even put you at a disadvantage, if the actual reload is significantly lower than what the mod predicts).
And lastly, as Quaksen already stated, the mods you use are only visible to your person (unless you're making a recording of it and publish it or you're streaming it in the first place).
When someone watches the same replay file on a different computer, they will see the vanilla version or anything modified by their own mods on their computer.