Do I need to use a stand-alone thermal overload to protect my motor when using a Jaguar drive?

 Generally no.  Jaguar inverters have built in electronic thermal overloads that can be scaled to correctly protect the motor. 
If however more than one motor is connected in parallel onto the output of the inverter then the Jaguar's internal overload can be either disabled or set to equal the total sum of the rated currents of each connected motor.
In this case, each motor must then be protected by a separate 'stand-alone' thermal overload, set at such a current level as to protect each motor from burn-out in the event of a fault. 
Each stand-alone thermal overload should have normally closed (n.c.) auxilliary contacts which can be connected in series and wired back to the Jaguar's control terminals.
One of these terminals can then be configured as a fault trip or 'THR' input.  Any motor in fault condition will then trip the Jaguar drive which will display an 'OH2' alarm.
Only when the fault has cleared can the Jaguar drive be reset.
See Jaguar instruction manuals for more detail.