I think it depends on the venue. If the venue is very simple I think they could look quite striking. It sounds like your venue is simple and that they tie in with your colour scheme. I think they will be great if so. If they are in a cluttered or cosy room, they might be a bit much. Can you tell us more about the decor? What is the floor made of?
Have you looked up albums of other people who got married there? Do you like how they look in those photos?
I think chair covers are absolutely disgusting. And a complete waste of money. I suppose thats a personal preference. I think they just look far too fussy so dont let my opinion put you off! I also cant stand those bamboo like white wash chairs you see everywhere at the moment.
To me it sounds/looks like they would work well