The steering tiller will never lock out the steering mechanism, it is connected with cables to the steering valve (talking non FBW a/c here).
You need to insert a steering pin in this valve to make sure no hydraulic power will actuate the valve and so the actuators and wheels.
During towing the tiller will follow nose gear angle, even if pin is installed, because of the cable connection.
If the pin is installed you cannot move the tiller by handforce though; you can move it if pin is removed. The wheels will only turn however when hydraulics are on.
Tiller movement will give you about 65° of wheel turning, rudder pedals less than 10°, all depending on a/c type. Tiller movement overrides rudder pedals (we taxi using the tiller to remain on a straight line while testing the rudder for free movement)
towing angles are also about 65° (red line on gear doors), so the wheel will not castor free when the steering pin is installed!!
To castor free a mechanic needs to disconnect the scissor links on the strut!