To allow administrators access to all volumes including the SMB shared folders, execute this Terminal command on the server:
sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.smb.server VirtualAdminShares -bool YES
To limit administrators to accessing only the SMB shared folders, execute this Terminal command on the server:
sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.smb.server VirtualAdminShares -bool NO
Restart the server after running the command. If rebooting the server is not convenient, you can un-share a currently shared folder and then re-share it, or share some other folder and then un-share it.