While we don't yet provide official support for Lego FTC / FRC controllers, the Pixy appears to be legal in these competitions.

User-created Pixy FTC Firmware is Here - https://github.com/Andrewiski/pixy

FTC App with Pixy Driver is Here - https://github.com/Andrewiski/ControlFreaks_ftc_app/tree/master/pixy
Also Includes an Arduino Test App as Proof of Concept.

Some users have ported the I2C library to RoboRio: https://github.com/Team5593/pixy

Here is some general info for FTC use: https://ftcforum.usfirst.org/forum/ftc-technology/android-studio/7211-i2c?p=44669#post44669