I TAS Touhou sometime, and i use a speedhack (Cheat Engine, MHS, ect)
The only thing i don't like when TASing Touhou, is you can't rerecord, so if you do Lunatic with one life and you die at the very last bullet of the last boss, you'll shit bricks.
Anyway, TAS are not legit if you compare that to non-tas, TASer only compete with each other or only for entertainment, so yeah, it is normally legit.
And like Slaves says, it's easy to tell when something is TAS