Vertical loft supports doing nothing?
Your picture suggests that they are different truss types. The fact that one doesn't have the vertical member in the middle doesn't mean that it isn't needed. I could design a roof without any bracing members - that doesn't mean that you can go and take out bracing members from a different roof. My design would need chunkier members and connections to take the different loads, whereas the roof with bracing members would have smaller members, as it will have been designed assuming those bracing members were there.

More than likely the reason it is there is because it is needed. But there's no problem with employing a structural engineer to confirm this.