SQL Server 2008 - combined index + other separate index on one column
The order of the columns in indexes is critical.
If your AdministratorUserId is the first column of the index, then separating the indexes will not improve anything.
The index works like an order by clause, meaning that it is sorted by the first column, then the second, then the third and so on. Because of that, an Index on AdministratorUserId is functionally equivalent to an index on AdministratorUserId and Name.  Note that it's possible in sql server to include columns to a non-clustered index that are non key columns. This will increase the storage size of the index but may improve performance of queries since it will save a lookup operation on columns that are included in the index.