Upload & Sell: Off
I can confirm a Clean and Check voucher cannot be used for lens calibration or adjustment. They'll probably dust off the outside elements for you, but I'm not sure what else they can do without taking it apart.
And as a side note, I've never had my gear cleaned and checked. Might be worth doing that someday.
Thank you for confirming that as I was contemplating sending a lens for cleaning and possible calibration. If they don't do anything beyond simple dusting of the outside of the lens, there is no sense in sending it in.