It isn't as straight forward as it seems...
I can only offer an opinion from a TC perspective but my understanding is;
Before we can give an aircraft a radar service from LTCC we have to ensure that the Mode A is validated and the Mode C is verified BUT
Some of the LTMA airfields have enhanced ATM procedures so departures from certain airfields will have had the Mode A validated and the Mode C verified by the AIR controller, examples of this are BB and GW but this doesn't apply to departures from LL and KK.
This could lead to some confusion-if you are a TMA North bod you would need to validate the Mode A of a LL departure but not a GW departure, you wouldn't need to do it for a SS BUZ because SS Fin will have done that for you but you would need to do it for a SS CLN because they (normally) come straight from the tower and SS aren't one of the units which validate it for you.
If in doubt I guess the safest thing to do is to get everyone to squawk IDENT becuase that way you don't have to remember which unit will or won't have done it for you. If the pilot squawks ident without asking and you don't challenge it you haven't complied with MATS Part 1 or 2
PS Ident is not required for DM purposes because departures from the LTMA auto DM.