Apple has either Unlisted Apps[1], Custom B2B apps[2], or Enterprise distribution apps[3].

All serve a slightly different purpose, but yes it would be possible to do but a pain to manage for most small businesses.

[1] https://developer.apple.com/support/unlisted-app-distributio... [2] https://developer.apple.com/custom-apps/ [3] https://developer.apple.com/programs/enterprise/