Does the Roku Streaming Stick 4K support dolby atmos?

Yes - all Roku player/soundbar/TV models support Dolby Atmos (DD+/Atmos, EAC3/JOC) playback (at a minimum via passthrough).

However, not all app versions/subscription levels support Atmos playback.

The app versions on the SS4K all support Atmos playback, just make sure you have the requisite subscription level for each app/service as well.