No you cannot track a FedEx delivery truck.
You can only track your own package to see if it's out for delivery but you cannot know where the delivery truck is or has been.
I'm sure though that FedEx has tracking devices on their trucks, vans and delivery vehicles but only for their use in case something happens and to know the stops and travel directions the delivery driver is going too and stopping at.
I've heard that you can track an Amazon delivery vehicle through Amazon but I have not tried it myself.
It would be nice to see where the FedEx and UPS trucks are but as of now it's not possible.