I think it’s not unusual for the Admin Console product to be managed by a different team -- for example, marketing ops might own or manage the workfront product while IT or security teams might manage the admin console product. This is especially true of the larger enterprises. If this describes your situation, I would suggest you work it out with your infosec or IT teams in terms of who and how they would allow to connect (rules, policies, etc.). Even if you’re running your own Admin Console, I still would advise you coordinate with IT/infosec as a CYA step, as it would be strange for IT to NOT have a policy about it (you’d want to get that in writing!).
In terms of adding non federated IDs or IDs federated elsewhere it hasn’t been a problem from the admin side (it’s fairly simple to manually add a new user and I’ve also worked for a number of companies that have at least added Adobe consultants.). From the user side, they might experience a slightly different login experience -- you could set up a screenshare with one and record it in order to provide training for other future users of the same type.