I've seen Apple's documentation about Enterprise Program Apps (see: Distributing Apple Developer Enterprise Program Apps)
I have an app that is made only for a specific user, say a store owner. And so that app can only be used by such owner. It's called the MyStore Admin (something like that). Basically it's like a CMS, used for managing all the users of the whole project and the data and everything for administrator. It's under the development.
Furthermore, I have a client app for his business that is on the App Store already and is available for everyone.
So back to my main question, can I submit the admin app to the App Store even though it can only be used by 1 person? They can't use the app unless they have an admin account provided by the company.
Yes we can publish the app.
Create one demo user and provide those details in iTunes description as well. So technically everyone can use the app. I also seen lot of apps like that. Make sure that demo account can able to access every feature of app.
And also can check your app meets these guidelines https://developer.apple.com/app-store/review/guidelines/#before-you-submit
Check this app for reference
https://itunes.apple.com/us/app/livecare-connectm/id1020817716?mt=8