I tried to play this video by using the Emby App in Nvidia Shield and also on web client.
And I enable the "Burn in SSA Subs for Formatting".
The Emby server will transcode the MKV file and burn the Subs.
But it will NOT use the font which embedded in the MKV file.
Here are the screen shot with the expected font in other media player:
expected_font.png 959.62KB 3 downloads
And here is the actual font in the Emby app:
actual_font.png 1004.07KB 3 downloads
Emby server version: 188.8.131.52
Emby app version: 1.7.43g