First, there is no issue with FC3/A/10C/UH-1H modules. The issue occur with M2000/Gazelle/Mig21bis (I don't test with other modules).
In MP the 6DOF for track-ir don't work but pitch/roll axes work.
We find that if you launch DCS with the track-ir in "pause mode", go multiplayer, and then enable track-ir once in cockpit it work...