I'd be more inclined to check your scheduling of jobs, rather than whether or not it is working in general. By adding a LUA into the mix, you further delay the defs getting to the SEPM, as you're adding an additional layer of abstraction.
Remember that Symantec typicall release up to 3 defs a day. With the LUA alone (running a D&D job every 4 hours) you're adding a delay of up to 4 hours. Add to that the default LU schedule on the SEPM is also typically every 4 hours, there is potential for a further 4 hour delay, resulting in an up-to 8 hours delay in defs getting to your SEPM (add to that your heartbeat intervals and download randomisation of clients, and we're looking at a day delay in defs getting to clients).
Have you co-ordinated the schedules of the LUA and SEPM? Have you considered increasing the frequency of each of their respective update jobs/runs?