The product page you linked to indicates that you should be able to power a Raspberry PI from the Adafruit Powerboost 1000c, so you probably do not need a separate regulator. You might consider posting on Adafruit’s support forum to see how they recommend connecting their Powerboost 1000c to the Raspberry Pi.
Thanks for the reply. I was planning to connect the output of powerboost to the slot where the pololu regulator is. There were 3 holes can i just connect it to ground and out?
You can connect an external 5V power source to the 5V and GND connection of our DRV8835 Dual Motor Driver to power the Raspberry Pi through its optional regulator connections as long as your power source can supply enough current to power the Raspberry Pi.