All other factors being equal, steels with aluminum necks may sound slightly different from those with wooden necks due to the amount of surface contact with the top deck.
Wooden necks are typically solid with a flat surface on the bottom.
Aluminum necks typically are designed to have several pockets of material relieved from the bottom either by machining of the material away or by designing pockets in the casting from which the necks are made. Aluminum necks will, therefore, make less contact with the top deck. The increase in mass described above may account for some of the differences in tone, with metal necks being brighter. Of course, the amount of torque on the screws used to attach the neck will give variations in sound also. Lastly, steels with metal necks may mount the pickups in a different manner than those with wooden necks.