Unfortunately, the answer to the question is "No." You do not have access to the "real" (i.e. -500) Administrator account in the hosted AWS Microsoft AD solution.
Thankfully, this limitation is clearly laid out by Amazon when researching the offering. I have not yet implemented it; we are just reviewing all of the various providers and options, and one of the first things in the FAQ for the service is a clear confirmation.
Amazon has put a lot of time in to preparing / automating this offering, and it requires a great deal of delegation of privileges and permissions so that Amazon's customer can have sufficient access to configure nearly all options of Active Directory while at the same time not allowing customer access to the AD management.
It follows that they would use these same methods to ensure best practices were being followed, specifically, that "Domain Admins" or privileged accounts used for managing AD should not be administrators on member computers.
Regardless, it makes sense - how could they properly guaranty up-time or support the offering if they granted the user the ability to hose the directory at any time?
In order to deliver a managed-service experience, AWS Microsoft AD must disallow operations by customers that would interfere with managing the service. Therefore, AWS does not provide Windows PowerShell access to directory instances, and it restricts access to directory objects, roles, and groups that require elevated privileges. AWS Microsoft AD does not allow direct host access to domain controllers via Telnet, Secure Shell (SSH), or Windows Remote Desktop Connection. When you create an AWS Microsoft AD directory, you are assigned an organizational unit (OU) and an administrative account with delegated administrative rights for the OU. You can create user accounts, groups, and policies within the OU by using standard Remote Server Administration Tools such as Active Directory Users and Groups.
Source: AWS Microsoft AD FAQ