I don't think it's actually a VLC problem, but since the vast amount of knowledge here, I still will ask it here:
When want to I play a 3D MKV with a subtitle I convert the .srt with "3DSubtitler" and that works fine for HSBS on active 3D screens since the subtitles are projected on both halves of the screen, with a slight difference for depth.
However, I can't use this for passive 3D monitors, since one screen is tilted 90 degrees to serve the polarized passive glasses.
Is there any way to produce subtitles for passive 3D monitors?