Maybe you can keep the sponge you bought to use for wheels & tires...then again, if it's going to mar, maybe not. CD test it or just take it back.
I'm not a pro, I only wash my cars but this time of year that's enough. I find the ONR doesn't quite clean the wheels perfectly...but close enough for winter. When I change back over to summer tires I'll hit the winter wheels with Eagle One All Wheel Cleaner & wax the wheels before I put them away. BTW I put some z16 on the tires several weeks ago, and with ONR washes the tires still look great!
Bottom line, for a customer's car that doesn't get regular attention, ONR is probably not going to cut it on the wheels.