I don't believe that LANDesk device groups are queryable. I think your best option here would be to first export all devices as a .CSV then export each device group as a CSV. Once you complete the export compile all of your CSV files into one spread sheet in Excel. You should now be able to hide duplicate entries and this will show you any devices that are not in one of your device groups.
I know it's about a year old but here goes ... this might get you and or someone else started:
select a1.UserName as 'Console User', a2.Member_Idn as 'Group Member IDN',
a3.Computer_Idn as 'Computer IDN', a3.DeviceName as 'Device Name',
a0.Name as 'Group Name'
from dbo.CustomGroup a0, ConsoleUser a1, CustomGroupComputer a2, Computer a3
where (a1.UserName like '%EnterConsoleUsernameHere%' and a0.Name = 'EnterSpecificGroupNameHere')
and a0.ConsoleUser_Idn = a1.ConsoleUser_Idn
and a0.CustomGroup_Idn = a2.CustomGroup_Idn
and a2.Member_Idn = a3.Computer_Idn
Works for LANDesk 9.5