For your example, no. I'll see if I can accurately represent a similar story.
Hey.com ran into that - they published an app which only presented a sign in prompt, with no mention or link to the external paid registration page.
Apple basically said the app was unusable without a separate paid account sign up, and if they wanted to completely gate functionality behind a subscription then they had to offer in-app purchasing as a subscription option.
There was much arguing about other apps, including other email apps, with the determination that the expectation was that those being enterprise focused had an excusion (e.g. that the user could not set up an email account via in-app purchasing, because the sales model was blocks of email seats for a company and not individual email accounts)
Thats why I said its easiest to consider Apple's subscription and in-app payment 'upgrade' cut to be about customer acquisition.
Hey turned around and added a feature - you could use the app without any registration to get a randomized (non vanity) email account with limited functionality. This met Apple's requirement (the app actually did something when people downloaded it) and Hey's requirement (to not give a penny to Apple in subscription revenue on moral grounds, even if there might be a business case for in-app purchasing leading to a much larger larger revenue base)