Helicopter flying - at least the basics, can be taught in a simulator if it has good visuals and a good mathematical model of the machine.
The visuals need to have lots of vertical cues (signs, posts, trees, fences, buildings), as opposed to just 'texture' (i.e. grass).
It also takes a lateral thinking instructor to make the simulator a good teaching tool.
We don't have much experience doing this, because until recently, we haven't had the tools to even start thinking of it.