pm2 status will show the current status; will not restart mm & omx_stream1.
You can try pm2 restart mm and see what happens.
Repeat
$ pstree -ap `pgrep omxplayer | head -1`; pstree -ap `pm2 status | grep omx_stream1 | awk '{print $10}'`
a few times.
I guess that you will see different PIDs and then status stopped (with pm2 status).
But perhaps it will remain stable.