The impression I get from these DLC characters is that giving them actual supports/integrating them into the game like standard characters would have been much more resource intensive compared to what IS was willing to invest here. They'd basically need to update the main game itself for that. The DLC characters basically seem to have been integrated into Awakening by tweaking the guest Avatar system, rather than allowing the addition of more "core" characters to the game. That can easily be seen by their models and their ability to be stored in the log book and, in the Japanese version, it was even more obvious because their generic quotes were the same as the "mute avatar" option (which was cut from the American release). Like I said before, the DLC chapters itself have tons of dialogue - each past unit has specific quotes with an Awakening character in addition to their generic ones, and yet none of that can be carried to the characters that the player actually gets due to the system they're using.
Even when they later made a DLC with 200 extra conversations for the core characters, they had to implement them as stage based conversations, rather than supports that can be reread at any time - even for pairs who lack supports in the main game. The new (and old) bgms from the DLC also aren't accessible through the sound test. Basically, none of Awakening's DLC seems to update/change the core game itself, just some specific points which were left "open" by the developers, like new portraits, stage specific features and apparently new classes.
