Correct, doesn't even need to be a box end wrench, if you put in into compression then a wrench with 2 open ends is fine. In fact, I would think that a wrench in compression (where the entire mass of the wrench is being used) would be stronger than a wrench in tension (where it's trying to tear the box end open).
VWVortex.com - torque settings for the pressure plate and flywheel.
Random website showing an example