Maybe:

Select IsNull(t1.ServerName,t2.ServerName) as ServerName,

IsNull(t1.ApplicationName,t2.ApplicationName) as ApplicationName,

Case

When t1.ApplicationName is null then 'Table2'

When t2.ApplicationName is null then 'Table1'

Else 'Combine'

End AppServer

From Table1 t1

Full Outer Join Table2 t2 on

(t1.ServerName = t2.ServerName) and (t1.ApplicationName = t2.ApplicationName)