The PCA chip is one of those I'm hoping to get around to writing a driver for as I've seen it used in a couple of places.
I have used the TLC5940 in the past and there is some information on my personal blog:
I decided to generate the clock (GSCLK) and Blank signals independently of the Netduino but you could use PWM pins on the Netduino for this.
I think you would need to write your own Servo class as things stand at the moment as you would be generating the PWM signals externally. If you decide to go down this route then why not look at how we have put Netduino.Foundation together and consider contributing to the library. We're always keen to accept pull requests from contributors.