How can I tell if a cable is rated for use as motor leads with a variable frequency drive?
You will probably need to follow specific recommendations published by VFD manufacturers. Also consider mitigation that might be available from the drive manufacturer built-in or added at the drive output. Detailed recommendations should be available from the large VFD manufacturers such as ABB, Rockwell / Allen Bradley, Yaskawa, Siemens, Eaton / Cutler-Hammer, Schneder / Square D / Télémécanique, and General Electric.

Gary Skibinski of Allen Bradley and John Bentley of ABB have written papers on the subject;

E. J. Bulington, S. Abney and G. L. Skibinski, "Cable alternatives for PWM AC drive applications," Industry Applications Society 46th Annual Petroleum and Chemical Technical Conference (Cat.No. 99CH37000), San Diego, CA, 1999, pp. 247-259.
doi: 10.1109/PCICON.1999.806443

J. M. Bentley and P. J. Link, "Evaluation of motor power cables for PWM AC drives," in IEEE Transactions on Industry Applications, vol. 33, no. 2, pp. 342-358, Mar/Apr 1997.
doi: 10.1109/28.567793