It works on my Oneplus Two on OxygenOS 3.0 Beta (6.0.1) all the way up to 192kHz.
One strange thing that I've noticed is that everything sounds A LOT better using hi-res audio 96 or 192kHz. Stable OxygenOS releases come with the MaxxAudio and this beta doesn't which has made the sound overall bad. It's not caused by the lack of equalization that could be done using MaxxAudio, it's more than that. Everything sounds compressed with distorted highs, lack of bass, no detail and lots of audible noise. This problem is still present while using 44,1 or 48kHz hi-res audio but with 96 or 192kHz it's completely gone and everything sounds as it should (if not better). I know this information might not be so relevant since the stable version of OxygenOS 3.0 will probably resolve the issue but it might be useful for others running 3.0 Beta.