To be honest, no. I’m sorry.
With Nuendo, it’s a two-step process because Nuendo only exports a stereo file when exporting video. Only the external Dolby Atmos renderer exports your video together with your Atmos mix in one step. (As an MP4 file with E-AC-3 JOC.)
But as you probably know, it’s standard practice that video and audio are encoded separately in consumer formats.
Yes, to play it back on an AV receiver, the Dolby Reference Player or a software player, you need to encode the ADM master file into a home theatre format.
No, you do not need to combine the E-AC-3 JOC or TrueHD with Atmos track with video. You can play the track directly with the Reference Player or MPC-HC. So if you are producing music with Atmos, you can also play the MLP file directly. (It may be necessary to mux it into an MKV container first so that the software player or hardware component can play the track.)