1- The brake system and the NWS are independent of each other. Each has its own hydraulic selector valves, no matter which hydraulic system supplies the NWS.
2- The BSCU does not use brake system information for the control of the NWS.
3- BUT: aside from the computer, you need hidraulic power.
On the ground with one engine running (and the towing lever of the electrical box in normal) the BSCU allows you to turn the nose wheel.... Provided it is hydraulicaly powered. Here we can find what you are looking for:
In the older version (with green hydraulic for NWS) if you have engine number two running, the PTU will power the green hydraulic only when the towing lever is in normal and the parking brake is released. I think that this condition is though for the case of a power push towing.
In the yellow hydraulic supplied NWS A320s, I guess you can move the nose wheel with the park brake set because you don't need the PTU.
Hope it helped