I can't find any documentation that states the admin shares don't work, but...
http://social.msdn.microsoft.com/Forums/...91-1cd64fa0db8b
I did find this: 
 Querying Remotely
The following are troubleshooting tips to help you query a remote machine. 
When I query a remote machine, nothing is found.
Remote queries fail when the machine name is longer than 15 bytes. This is a known issue, and the only workaround is to give the remote machine a shorter name.
When I query a remote machine as admin, nothing is found.
In order to query a remote machine, the folder you want to search must be shared even if you access it as admin. Sharing is a prerequisite for querying. First, share the folder to yourself, and then you can query it remotely.
 
http://technet.microsoft.com/en-us/library/cc771814(WS.10).aspx