For regular Alldevice accounts you would need to have a separate login for each account. This means a differing username and password for each separate account.
Multi Licence / Sites
The only time this isn't true is when the account is a multi site account, where different companies typically owned by the same group, and in one region are all added to a single Alldevice instance. Then depending on your rights you can login to one or multiple companies in the single instance.
For example here is an account with 4 companies / sites which I have access rights to all.
