Is collectstatic command necessary if application only serves media files?
Your Django-based service does not need collectstatic at all.
Question is about django admin - because admin app uses static content css/img/js.
Do you use django admin in production? 

If yes - then you need to run collectstatic command it, otherwise admin site will be unstyled or totally broken because of missing js files.
If no - then you collectstatic command has no use for you.
A Django-based service that I'm working on allows users to upload media files via REST API or Django admin but does not provide or use any static files (like css styles, js libraries, etc.).
Media files are stored in specific fields in database and use S3 bucket as storage backend so server itself does not directly serve any files at all.
Having such a case is running collectstatic command required every time application is being deployed?
Thought the concept of static and media files in Django application is rather simple I'm still confused about whether configurations for them should be somehow related?