"As far as those 3V/80mA Sparkfun vibration motors are concerned, they seem to run fine at 500Hz, ramping up and down smoothly, based on prior experience. Alas, I won't be able to confirm with the TLC5940 for at least two weeks (vacation)."
I've used the TLC5940 to drive motors... a tip that usually emerges is to use diodes to protect the chip from any reverse current from the motors. I've used the tlc5940 with motors with diodes and without, and it never harmed the arduino or tlc5940 but it's good to use as a precaution