Question:
Can I have groups with the same name as users?
Or, vice-versa:
Can I have users with the same name as groups?
Answer
No it is not possible.
Microsoft denies to have groups and users the same sAMAccountName as it has to be unique in an ActiveDirectory domain.
Therefore, in UCS domains with Samba we follow this restrictions and do not allow groups to have the same name as a user account.
Even in environments with no Samba installed this is not allowed as the (possibly later) install of Samba would cause severe synchronization issues.