So the below should give you only ENABLED assets based on their AD Status (since last scan), is this not working for you ?
Also do you have the Server options set for "Remove users disabled in Active Directory from the Lansweeper database" ?
Select Top 1000000 tblADusers.Username,
tblADusers.IsEnabled,
tblADusers.Name
From tblADusers
Where tblADusers.IsEnabled = 'true'