The dot correction thing just might work. I originally overlooked the TLC5941, because the regular grayscale using PWM seemed a little slow. (At the maximum PWM grayscale clock speed of 30MHz, the 12bit counter overflows at a rate of 7.3KHz. The POV display has to change what's output on the LEDs at about the same rate, so the PWM would in effect just be setting the on-time of the LED, or the width of each "pixel".) Theoretically, though, even the regular PWM should work for producing grayscale.
Using the 6-bit dot correction definitely seems faster though, and closer to actual grayscale. It's not completely clear from the data sheet how dot correction implemented, but from the block diagram, it looks like it's definitely not PWM. A 6-bit R-2R ladder to control the current sink wouldn't be that hard to do. Accuracy/linearity isn't really that big of a concern for me.