EXISTS <Registry Value> "HKLM\System\CurrentControlSet\Services\Lanmanserver\Shares\\downloads"
You can create a configuration group to find out which workstation computers have administrative shares enabled:
NOT EXISTS <Registry Value> "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters\\AutoShareWks" OR <Registry Value> "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters\\AutoShareWks" = "1"
Here's the same rule, only for servers:
NOT EXISTS <Registry Value> "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters\\AutoShareServer" OR <Registry Value> "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters\\AutoShareServer" = "1"
Hopefully this gives you the information you need.