I was thinking the same. I had the same wheel sizes with ET32 fronts & ET30 rears and I had very little space to the front coilovers (less than 2-4mm) but had about 10-15mm going spare at the rear.... The DW CS2's are meant to give better than standard clearance for wheels too over other coilovers as they are inversly mounted....
I did have the stretch the tyres a bit though to get them to fit under the standard arches...
Edit;
Spec S S15
Spacers: none
Suspension: Driftworks CS2's
Comments: standard arches
Wheels: Work CR Kai
Size: 17x8JJ ET 32 Front and 17x9JJ Rears ET 30
Tyres: Hankook Ventus 215/45r17 front and 225/45r17 rear
Did you check out the Wheel fitment guide?
http://forum.s15oc.com/showthread.php?556-Ultimate-wheel-fitting-guide/page28