Okay so the reason why this happens is thus:
In the scenario described there are two accounts but they are managed completely different.
The first account is managed strictly in DTM so DTM decides who has access.
The second account where it says you do not have access you must login to the Cloud is because the check box for permissions to be handled through the Cloud is turned on. On the second account the user is expected to login via the Cloud in order for them to gain access to set the permissions.
Presently working as expected here. It looks weird since one is grayed out and the other is active. It all depends on where you login. When the permissions are managed through the Cloud its expecting you go through marketing.adobe.com not through dtm.adobe.com for login. Make sense?