17 inch Rota RB wheels and JCW Brakes do they fit?

[BIRMA]

I've been looking at several USA based Mini forum photo's to see if the JCW front discs and callipers fit OK with 17 inch Rota RB's. As far as I can see they do but one car had 15mm spacers fitted, am I right in thinking this was perhaps just to give a wider appearance rather than necessity?
I may retro fit a JCW brake package to my Clubvan but before doing so better check if there will be no problems.