For VFD motor it is also suggested to check its electrical current.
vibration analysis also helps in motor condition evaluation because it gives vibration amplitude at 2xelectrical line frequency but its magnitude limit really matters. Analysing softwares limit 2xFL frequency amplitude and we should follow these limit.
other frequencies include bearing faults, rotor bar/slot faults, etc also indicate motor condition.
for vibration analysis of VFD motor, it is recommended to operate it on fixed rpm during inspection atleast.