Hi, I also recently noticed that the description in the tutorial is a bit misleading, as the base_footprint described there is not rigidly attached to the robot as it is the case with most robot models out there. I'll have to think about how improve the description :)
Now for your specific problem: Yes, you have to get to transform from the IMU published to tf. If your robot actually experiences significant roll/pitch motion, that is. If it doesn't, the 'base_stabilized' frame is not needed, as described in the tutorial.
I uploaded a very simple helper node for publishing roll/pitch attitude data from imu to tf just a few minutes ago here (not yet indexed on ros.org).
So what should work is the following: Copy/Use the example.launch and use your imu topic there. For the base_frame you have to use a body-fixed frame of your robot, let's use 'base_footprint' as an example. You now only have to get your odometry publisher to publish 'base_stabilized → odom' instead of 'base_footprint → odom'.
For hector_mapping you can then set the following parameters:
<param name="pub_map_odom_transform" value="true"/>
<param name="map_frame" value="map" />
<param name="base_frame" value="base_stabilized" />
<param name="odom_frame" value="odom" />
Let me know if that works for you.
