It depends. The VFD becomes the SCPD for the motor circuit in most cases (some cheap mfrs don't test it that way with UL and instead, bury some little fine print in the installation manual saying that the installer is responsible for the motor SCPD). So if you have a 250HP motor and a 300HP VFD, the motor lead conductors can be sized for the motor. But if you ever changed the motor to 300HP, then you would have to change the conductors too so it's never a bad thing to think ahead if there is any possibility it might change.
But the NEC does say that the LINE side conductors feeding the VFD must be sized for 125% of the VFD Max Amp rating, not the motor connected to it. That may be where the confusion lies.
Side note:
Not sure where you would need a 300HP VFD for a 225HP motor by the way. If the 225HP motor (not that there is such a thing) was insufficient for the load, a bigger VFD would not solve the problem. On really rare occasions you may need a bigger VFD if you need full Breakdown Torque from the motor for longer than the VFD can deliver it, but in most of those cases a standard motor will not be able to deliver it for longer anyway, so you are looking at a complete engineered drive / motor situation. I've seen that on SAG Mills and big centrifuges, but it's not common by any stretch. I know there are people who believe in over sizing everything (and the VFD mfrs love them), but it really isn't necessary most of the time.
