The accelerometer is only exposed because SDL exposes it as a 3-axis joystick. It doesn't expose the gyroscope. I have plans to add more sensor (accelerometer, gyro, etc) functionality to SDL, but no work has been done yet.
In any case, I strongly feel that platform API usage such as phone sensors should go through SDL, since that's its purpose.
If I were to assist with this, where do I begin? The files in SDL I mean.