Just to clarify: the number of LMS workers defined by OPENEDX_LMS_UWSGI_WORKERS is actually the number of processes launched by uwsgi for the web server: uWSGI Options — uWSGI 2.0 documentation
You can check how many processes are running for each uwsgi server by running:
$ ps aux | grep processes
On my machine, with the default configuration, I get --processes=2:
regis 64201 0.0 0.0 2616 484 ? Ss 08:35 0:00 /bin/sh -c uwsgi --static-map /static=/openedx/staticfiles/ --static-map /media=/openedx/media/ --http 0.0.0.0:8000 --thunder-lock --single-interpreter --enable-threads --processes=${UWSGI_WORKERS:-2} --buffer-size=8192 --wsgi-file $SERVICE_VARIANT/wsgi.py
regis 64259 2.7 1.1 1157876 244612 ? Sl 08:35 0:06 uwsgi --static-map /static=/openedx/staticfiles/ --static-map /media=/openedx/media/ --http 0.0.0.0:8000 --thunder-lock --single-interpreter --enable-threads --processes=2 --buffer-size=8192 --wsgi-file lms/wsgi.py
regis 64275 0.0 0.0 54388 9064 ? S 08:35 0:00 uwsgi --static-map /static=/openedx/staticfiles/ --static-map /media=/openedx/media/ --http 0.0.0.0:8000 --thunder-lock --single-interpreter --enable-threads --processes=2 --buffer-size=8192 --wsgi-file lms/wsgi.py
regis 65433 0.0 1.1 1157876 227200 ? S 08:35 0:00 uwsgi --static-map /static=/openedx/staticfiles/ --static-map /media=/openedx/media/ --http 0.0.0.0:8000 --thunder-lock --single-interpreter --enable-threads --processes=2 --buffer-size=8192 --wsgi-file lms/wsgi.py
regis 70562 0.0 0.0 9048 1716 pts/1 S+ 08:39 0:00 grep --color=auto processes