I don't use the registration queue myself.
But I believe you need to give them control panel access.
Control Panel ยป Group Management
select the cp link to the right of global moderator
Not sure which option to pick but try the
Can edit users
Just place a 1 in the field.
Update:
I just tried this in version 7.5.6
It does not work even with full cp access.
The only way is to make them a admin.
Last edited by Ruben; 06/03/2011 6:21 PM. Reason: added update