I believe we have some EE's among us, and maybe they can give you a condensed explanation of the phenomenon you're protecting against, but if you want to wade through some technical reading, here's a couple of sites for you:
http://www.allaboutcircuits.com/vol_1/chpt_13/2.html
http://www.nhavfd.com/tech-stuff/dvdt-output-filters/
In particular, I will quote a paragraph from the second reference:
"It’s also important to note that 230 volt 3 phase motors are adequately protected from failure due to voltage overshoot by present insulation standards. Keep in mind the maximum voltage that is possible
Example: 230 input volts x 1.1 = 253 x 1.414 = 357.7 x 2 = 715.4 possible volts.
Most motors are rated for both 230 & 460 volts. So the maximum output voltage from a VFD running 230 volts is well below the NEMA standards MG-1 of 1600 volts used today. In other words if your system voltage is 230, motor failure is very rare when using a VFD, but it can still fail."
End quote
Please note that they do refer to "present" NEMA standards, but if indeed your motor is a dual 230/460 voltage motor, and the leads are short (in this context, probably meaning <100 feet), you are unlikely to see spikes that are a real threat.