NAVX angled mounting

My team has is not sure whether or not we can still receive the proper values from the gyro if we mount the robo Rio at an angle instead of it being along the x or y-axis.

OmniMount might work for you, but it does require an axis perpendicular to the ground.
If that doesn’t fit your setup, you might be able to use some math to calculate the actual angles of each robot-relative axis. I would probably try converting the angles given by the NavX to a point vector, and using a rotation matrix corresponding to the mounting angle of the NavX to give you real world angles.