IMU data is streamed to the configured port of your machine via UDP, by default it's port 7502 for Lidar packets and port 7503 for IMU packets. I'm not sure about ROS solution, but can tell you that Ouster Studio does not yet capture IMU packets, which is (besides performance) the major reason I wrote (so far: hacked) my own capture program with Qt/C++. Sorry, but I cannot share the code in current state, but it was straight-forward following the SW user guide.
The "imu_intrinsics" are important if you want to translate IMU readings to global Lidar coordinate system - the IMU is not placed at center of Lidar. For my Lidar it's a translation by (6.253 ; -11.775 ; 7.645) .
I hope this helps you getting further,