I don’t know if you ever found a solution to this but this is what we found works to solve the problem.
In our dcc tool we created two sets of wheel bones placed at the pivot for the wheels. One set is the PhysX simulated wheels while the other set drive the visual wheel mesh primitives. During the vehicle setup assign the PhysX simulated bones to the vehicle movement component under wheel setups. Inside the vehicle animation blueprint we first call the Wheel Handler node to update the PhysX simulated bones then copy the rotation and translation to the visual bones. As strange as it seems this allows you to perform correct motion blur on the wheels.
In the camera for the vehicle we found these motion blur settings to work well for our setups.
Amount: 0.5
Max size: 0.75
Per Object Size: 0.5
These may need to adjusted for your camera and mesh setup.
The double wishbone suspension tutorial goes into the details of how to perform the copies from the PhysX simulated bones to the visual bones.
Here is a pic of our animation blueprint. It includes the double wishbone setup. the first four CopyBone nodes copy the data from the PhysX wheel to the corresponding Visual Wheel. Note: The steering of the front wheels is part of the PhysX simulation.
Hope this helps others trying to implement wheeled vehicles and runs into the motion blur problem.