Hello,
I just ran into this issue, and using the information dancode provided solved it (in Blueprint).
So I can confirm the controller pitch and yaw are indeed both replicated and available via Get Base Aim Rotation.
I am lazy and so using a control rig for the look-at behaviour, which is easiest implemented with a target point, so my fixed (network friendly) version of setting this target point now looks like this:
and works well. Looking at it again, probably the select is unnecessary and you could just use Get Base Aim Rotation always.
If you explicitly need yaw (from actor forward) to feed into a Aim Offset, you will need to do the transform dancode provided on it.
Edit: My bad. Yaw was not coming through, I was seeing things.
This post was very insightful, and with modifications got my project fixed up properly (nutshell version: what we want is replicated to the server, but no further, so you unavoidably need to get your hands dirty here).