Edit: Looks like it only supports custom video encoders and not a muxed output.
For what it's worth, here's my input on the matter:
I personally never really export a finished clip from Resolve, but only use the option for individual clips to export a grade, the Online is then done somewhere else.
But even for this, it would help tremendously to have custom options (like Prores and others on Windows). So, just my two cents on the matter 
Danke Dir herzlich für die viele Arbeit